In PGO build, the improvement is not much.

(3.9 branch, with PGO, build.bat -p X64 --pgo)

+-------------------------+--------------+------------------------------+
| Benchmark               | baseline-pgo | ob3-pgo                      |
+=========================+==============+==============================+
| 2to3                    | 464 ms       | 462 ms: 1.01x faster (-1%)   |
+-------------------------+--------------+------------------------------+
| chameleon               | 14.0 ms      | 13.5 ms: 1.03x faster (-3%)  |
+-------------------------+--------------+------------------------------+
| crypto_pyaes            | 142 ms       | 143 ms: 1.00x slower (+0%)   |
+-------------------------+--------------+------------------------------+
| django_template         | 65.0 ms      | 65.4 ms: 1.01x slower (+1%)  |
+-------------------------+--------------+------------------------------+
| fannkuch                | 665 ms       | 650 ms: 1.02x faster (-2%)   |
+-------------------------+--------------+------------------------------+
| float                   | 166 ms       | 164 ms: 1.01x faster (-1%)   |
+-------------------------+--------------+------------------------------+
| genshi_text             | 41.4 ms      | 41.0 ms: 1.01x faster (-1%)  |
+-------------------------+--------------+------------------------------+
| genshi_xml              | 88.1 ms      | 87.0 ms: 1.01x faster (-1%)  |
+-------------------------+--------------+------------------------------+
| go                      | 315 ms       | 311 ms: 1.01x faster (-1%)   |
+-------------------------+--------------+------------------------------+
| hexiom                  | 12.7 ms      | 12.6 ms: 1.01x faster (-1%)  |
+-------------------------+--------------+------------------------------+
| json_dumps              | 16.7 ms      | 16.6 ms: 1.01x faster (-1%)  |
+-------------------------+--------------+------------------------------+
| json_loads              | 33.5 us      | 32.1 us: 1.04x faster (-4%)  |
+-------------------------+--------------+------------------------------+
| logging_simple          | 13.6 us      | 13.3 us: 1.02x faster (-2%)  |
+-------------------------+--------------+------------------------------+
| mako                    | 22.7 ms      | 22.8 ms: 1.01x slower (+1%)  |
+-------------------------+--------------+------------------------------+
| meteor_contest          | 136 ms       | 138 ms: 1.01x slower (+1%)   |
+-------------------------+--------------+------------------------------+
| nbody                   | 189 ms       | 186 ms: 1.02x faster (-2%)   |
+-------------------------+--------------+------------------------------+
| nqueens                 | 135 ms       | 135 ms: 1.01x faster (-1%)   |
+-------------------------+--------------+------------------------------+
| pathlib                 | 157 ms       | 154 ms: 1.02x faster (-2%)   |
+-------------------------+--------------+------------------------------+
| pickle                  | 16.8 us      | 16.4 us: 1.02x faster (-2%)  |
+-------------------------+--------------+------------------------------+
| pickle_dict             | 41.3 us      | 40.4 us: 1.02x faster (-2%)  |
+-------------------------+--------------+------------------------------+
| pickle_list             | 6.34 us      | 6.42 us: 1.01x slower (+1%)  |
+-------------------------+--------------+------------------------------+
| pickle_pure_python      | 588 us       | 584 us: 1.01x faster (-1%)   |
+-------------------------+--------------+------------------------------+
| pidigits                | 242 ms       | 242 ms: 1.00x faster (-0%)   |
+-------------------------+--------------+------------------------------+
| pyflate                 | 905 ms       | 898 ms: 1.01x faster (-1%)   |
+-------------------------+--------------+------------------------------+
| python_startup          | 28.0 ms      | 27.9 ms: 1.00x faster (-0%)  |
+-------------------------+--------------+------------------------------+
| regex_compile           | 220 ms       | 218 ms: 1.01x faster (-1%)   |
+-------------------------+--------------+------------------------------+
| regex_v8                | 33.1 ms      | 32.9 ms: 1.01x faster (-1%)  |
+-------------------------+--------------+------------------------------+
| richards                | 88.9 ms      | 88.3 ms: 1.01x faster (-1%)  |
+-------------------------+--------------+------------------------------+
| scimark_fft             | 494 ms       | 486 ms: 1.02x faster (-2%)   |
+-------------------------+--------------+------------------------------+
| scimark_lu              | 210 ms       | 207 ms: 1.02x faster (-2%)   |
+-------------------------+--------------+------------------------------+
| scimark_monte_carlo     | 141 ms       | 137 ms: 1.03x faster (-3%)   |
+-------------------------+--------------+------------------------------+
| scimark_sor             | 263 ms       | 255 ms: 1.03x faster (-3%)   |
+-------------------------+--------------+------------------------------+
| scimark_sparse_mat_mult | 6.48 ms      | 6.10 ms: 1.06x faster (-6%)  |
+-------------------------+--------------+------------------------------+
| spectral_norm           | 200 ms       | 184 ms: 1.09x faster (-8%)   |
+-------------------------+--------------+------------------------------+
| sqlalchemy_imperative   | 39.4 ms      | 37.8 ms: 1.04x faster (-4%)  |
+-------------------------+--------------+------------------------------+
| sqlite_synth            | 4.24 us      | 4.31 us: 1.02x slower (+2%)  |
+-------------------------+--------------+------------------------------+
| sympy_sum               | 266 ms       | 270 ms: 1.01x slower (+1%)   |
+-------------------------+--------------+------------------------------+
| sympy_str               | 416 ms       | 418 ms: 1.00x slower (+0%)   |
+-------------------------+--------------+------------------------------+
| telco                   | 8.12 ms      | 8.28 ms: 1.02x slower (+2%)  |
+-------------------------+--------------+------------------------------+
| unpack_sequence         | 92.3 ns      | 80.8 ns: 1.14x faster (-13%) |
+-------------------------+--------------+------------------------------+
| unpickle                | 17.9 us      | 18.3 us: 1.02x slower (+2%)  |
+-------------------------+--------------+------------------------------+
| unpickle_list           | 6.43 us      | 6.57 us: 1.02x slower (+2%)  |
+-------------------------+--------------+------------------------------+
| unpickle_pure_python    | 419 us       | 414 us: 1.01x faster (-1%)   |
+-------------------------+--------------+------------------------------+
| xml_etree_parse         | 184 ms       | 183 ms: 1.00x faster (-0%)   |
+-------------------------+--------------+------------------------------+
| xml_etree_iterparse     | 135 ms       | 134 ms: 1.01x faster (-1%)   |
+-------------------------+--------------+------------------------------+
| xml_etree_generate      | 130 ms       | 129 ms: 1.01x faster (-1%)   |
+-------------------------+--------------+------------------------------+
| xml_etree_process       | 101 ms       | 99.4 ms: 1.01x faster (-1%)  |
+-------------------------+--------------+------------------------------+

Not significant (13): chaos; deltablue; dulwich_log; logging_format; logging_silent; python_startup_no_site; raytrace; regex_dna; regex_effbot; sqlalchemy_declarative; sympy_expand; sympy_integrate; tornado_http