Disabling Spectre V2 Mitigations Is What Can Impair AMD Ryzen 7000 Series Performance

At least from this round of testing we now know that it's specifically the Spectre V2 mitigation that should be left on for Zen 4 to avoid hurting the performance, the opposite of what we are used to seeing with prior processor families.

As for why the Ryzen 7000 series performance is actually slower if disabling the Spectre V2 mitigations, that's likely something only AMD can effectively answer but presumably comes down to Zen 4 being better tuned/optimized now for assuming the Spectre V2 mitigated behavior in the micro-architecture. In any event this is ultimately good news for end users and those with production systems should be running in the default (secure) state rather than trying to run "mitigations=off" mode.

Those interested can see all of my mitigation tests from the AMD Ryzen 5 7600X on Linux 6.0 via this result page.