IF maxes around ~2GHz on current chips so it is impossible to run it 1:1 on anything faster than DDR5-4000, but apparently something was improved along the way, and optimal RAM speed is at mentioned 6000 and not matching doesn't hurt as much in Zen 4

At least from this test https://www.hardwaretimes.com/ddr5-6000-memory-and-2000mhz-f...

it appears that even with mismatched clock (the 2166 IB with 6000MHz memory) latency continues to drop, and problems start if you try to run memory controller above that