I run the pyperformance test suite with PGO + LTO + full cpu isolation in the speed.python.org machine and these were the results:

+-------------------------+--------------------------------------+---------------------------------------+
| Benchmark               | master                               | immortal_refs_patch                   |
+=========================+======================================+=======================================+
| pidigits                | 289 ms                               | 290 ms: 1.01x slower (+1%)            |
+-------------------------+--------------------------------------+---------------------------------------+
| pickle                  | 20.2 us                              | 20.3 us: 1.01x slower (+1%)           |
+-------------------------+--------------------------------------+---------------------------------------+
| xml_etree_parse         | 253 ms                               | 258 ms: 1.02x slower (+2%)            |
+-------------------------+--------------------------------------+---------------------------------------+
| json_loads              | 52.0 us                              | 53.1 us: 1.02x slower (+2%)           |
+-------------------------+--------------------------------------+---------------------------------------+
| scimark_fft             | 708 ms                               | 723 ms: 1.02x slower (+2%)            |
+-------------------------+--------------------------------------+---------------------------------------+
| python_startup_no_site  | 7.83 ms                              | 8.04 ms: 1.03x slower (+3%)           |
+-------------------------+--------------------------------------+---------------------------------------+
| scimark_sparse_mat_mult | 9.28 ms                              | 9.57 ms: 1.03x slower (+3%)           |
+-------------------------+--------------------------------------+---------------------------------------+
| unpickle                | 28.0 us                              | 28.9 us: 1.03x slower (+3%)           |
+-------------------------+--------------------------------------+---------------------------------------+
| regex_effbot            | 4.70 ms                              | 4.86 ms: 1.03x slower (+3%)           |
+-------------------------+--------------------------------------+---------------------------------------+
| xml_etree_iterparse     | 178 ms                               | 184 ms: 1.04x slower (+4%)            |
+-------------------------+--------------------------------------+---------------------------------------+
| python_startup          | 11.5 ms                              | 12.0 ms: 1.04x slower (+4%)           |
+-------------------------+--------------------------------------+---------------------------------------+
| scimark_monte_carlo     | 212 ms                               | 221 ms: 1.04x slower (+4%)            |
+-------------------------+--------------------------------------+---------------------------------------+
| pathlib                 | 38.6 ms                              | 40.5 ms: 1.05x slower (+5%)           |
+-------------------------+--------------------------------------+---------------------------------------+
| sqlite_synth            | 7.85 us                              | 8.26 us: 1.05x slower (+5%)           |
+-------------------------+--------------------------------------+---------------------------------------+
| sqlalchemy_imperative   | 62.9 ms                              | 66.2 ms: 1.05x slower (+5%)           |
+-------------------------+--------------------------------------+---------------------------------------+
| richards                | 138 ms                               | 145 ms: 1.05x slower (+5%)            |
+-------------------------+--------------------------------------+---------------------------------------+
| crypto_pyaes            | 199 ms                               | 210 ms: 1.06x slower (+6%)            |
+-------------------------+--------------------------------------+---------------------------------------+
| nbody                   | 249 ms                               | 265 ms: 1.06x slower (+6%)            |
+-------------------------+--------------------------------------+---------------------------------------+
| raytrace                | 937 ms                               | 995 ms: 1.06x slower (+6%)            |
+-------------------------+--------------------------------------+---------------------------------------+
| deltablue               | 13.4 ms                              | 14.2 ms: 1.06x slower (+6%)           |
+-------------------------+--------------------------------------+---------------------------------------+
| tornado_http            | 276 ms                               | 295 ms: 1.07x slower (+7%)            |
+-------------------------+--------------------------------------+---------------------------------------+
| scimark_lu              | 247 ms                               | 264 ms: 1.07x slower (+7%)            |
+-------------------------+--------------------------------------+---------------------------------------+
| sqlalchemy_declarative  | 280 ms                               | 300 ms: 1.07x slower (+7%)            |
+-------------------------+--------------------------------------+---------------------------------------+
| dulwich_log             | 143 ms                               | 153 ms: 1.07x slower (+7%)            |
+-------------------------+--------------------------------------+---------------------------------------+
| chaos                   | 210 ms                               | 226 ms: 1.07x slower (+7%)            |
+-------------------------+--------------------------------------+---------------------------------------+
| 2to3                    | 594 ms                               | 639 ms: 1.08x slower (+8%)            |
+-------------------------+--------------------------------------+---------------------------------------+
| unpickle_list           | 6.60 us                              | 7.10 us: 1.08x slower (+8%)           |
+-------------------------+--------------------------------------+---------------------------------------+
| float                   | 213 ms                               | 229 ms: 1.08x slower (+8%)            |
+-------------------------+--------------------------------------+---------------------------------------+
| pyflate                 | 1.27 sec                             | 1.37 sec: 1.08x slower (+8%)          |
+-------------------------+--------------------------------------+---------------------------------------+
| go                      | 481 ms                               | 522 ms: 1.09x slower (+9%)            |
+-------------------------+--------------------------------------+---------------------------------------+
| pickle_pure_python      | 966 us                               | 1.05 ms: 1.09x slower (+9%)           |
+-------------------------+--------------------------------------+---------------------------------------+
| meteor_contest          | 175 ms                               | 191 ms: 1.09x slower (+9%)            |
+-------------------------+--------------------------------------+---------------------------------------+
| genshi_xml              | 148 ms                               | 161 ms: 1.09x slower (+9%)            |
+-------------------------+--------------------------------------+---------------------------------------+
| chameleon               | 20.6 ms                              | 22.5 ms: 1.09x slower (+9%)           |
+-------------------------+--------------------------------------+---------------------------------------+
| nqueens                 | 191 ms                               | 208 ms: 1.09x slower (+9%)            |
+-------------------------+--------------------------------------+---------------------------------------+
| telco                   | 14.6 ms                              | 16.0 ms: 1.09x slower (+9%)           |
+-------------------------+--------------------------------------+---------------------------------------+
| logging_format          | 22.1 us                              | 24.2 us: 1.10x slower (+10%)          |
+-------------------------+--------------------------------------+---------------------------------------+
| regex_compile           | 322 ms                               | 355 ms: 1.10x slower (+10%)           |
+-------------------------+--------------------------------------+---------------------------------------+
| hexiom                  | 16.4 ms                              | 18.1 ms: 1.10x slower (+10%)          |
+-------------------------+--------------------------------------+---------------------------------------+
| json_dumps              | 25.6 ms                              | 28.3 ms: 1.10x slower (+10%)          |
+-------------------------+--------------------------------------+---------------------------------------+
| sympy_sum               | 397 ms                               | 439 ms: 1.11x slower (+11%)           |
+-------------------------+--------------------------------------+---------------------------------------+
| sympy_integrate         | 42.7 ms                              | 47.2 ms: 1.11x slower (+11%)          |
+-------------------------+--------------------------------------+---------------------------------------+
| django_template         | 120 ms                               | 133 ms: 1.11x slower (+11%)           |
+-------------------------+--------------------------------------+---------------------------------------+
| sympy_str               | 633 ms                               | 702 ms: 1.11x slower (+11%)           |
+-------------------------+--------------------------------------+---------------------------------------+
| xml_etree_generate      | 162 ms                               | 180 ms: 1.11x slower (+11%)           |
+-------------------------+--------------------------------------+---------------------------------------+
| spectral_norm           | 244 ms                               | 272 ms: 1.11x slower (+11%)           |
+-------------------------+--------------------------------------+---------------------------------------+
| xml_etree_process       | 134 ms                               | 149 ms: 1.11x slower (+11%)           |
+-------------------------+--------------------------------------+---------------------------------------+
| logging_simple          | 19.3 us                              | 21.5 us: 1.11x slower (+11%)          |
+-------------------------+--------------------------------------+---------------------------------------+
| mako                    | 28.2 ms                              | 31.5 ms: 1.12x slower (+12%)          |
+-------------------------+--------------------------------------+---------------------------------------+
| fannkuch                | 853 ms                               | 954 ms: 1.12x slower (+12%)           |
+-------------------------+--------------------------------------+---------------------------------------+
| sympy_expand            | 983 ms                               | 1.11 sec: 1.13x slower (+13%)         |
+-------------------------+--------------------------------------+---------------------------------------+
| genshi_text             | 64.0 ms                              | 72.9 ms: 1.14x slower (+14%)          |
+-------------------------+--------------------------------------+---------------------------------------+
| unpack_sequence         | 123 ns                               | 142 ns: 1.16x slower (+16%)           |
+-------------------------+--------------------------------------+---------------------------------------+
| logging_silent          | 311 ns                               | 364 ns: 1.17x slower (+17%)           |
+-------------------------+--------------------------------------+---------------------------------------+
| unpickle_pure_python    | 581 us                               | 683 us: 1.17x slower (+17%)           |
+-------------------------+--------------------------------------+---------------------------------------+

Not significant (2): pickle_list; regex_dna; pickle_dict; scimark_sor; regex_v8