Running Tools/scripts/var_access_benchmark.py on the production macOS builds on python.org shows a performance drop-off between alpha-7 and beta-1.

Apple Silicon
-------------
read local            4.1ns ->  4.5ns
read non_local        4.1ns ->  4.6ns
read global           4.2ns ->  4.9ns
read builtin          4.2ns ->  5.3ns
classvar from cls    10.1ns -> 12.6ns
classvar from inst    9.5      11.7
read instvar          9.2      11.3
instvar with slots    5.8       8.2
namedtuple           11.1      14.2
  ...

Since the effects are seen in almost every category, I suspect a build problem, a change to the eval loop, or a failure to inline some of the shared functions that used to be macros.