Guide: OpenCore Install Guide (link).

The advice to use iMac20,x SMBIOS with frequency vectors results in Apple Comet Lake frequency vectors being used. There you would find QoS values that are heavily limited to at least somewhat fit the TDP of Apple iMac cases. While we mostly tested that on Rocket Lake (11700k) with @vandroiy2013, the results with Comet Lake should be the same. The performance loss due to such a configuration on a fully unlocked setup results in up to 50% performance loss under synthetic and real-world tasks.

The solution is to inject proper frequency vectors as I explained on AppleLife. The supplied file should be useable on Comet Lake, Rocket Lake, and Alder Lake setups. Perhaps it will also be useable on older generations, but I'd recommend testing these through trial and error.

The easy way to determine whether you have performance drains is to disable SSDT-PLUG and run some tasks or benchmarks. You will see noticeably worse results if your system is affected.

The relevant values in question look like this. The first screenshot is the iMac20,1 QoS for the kernel and the second screenshot is the fixed version, based on the Haswell QoS we made some time with @Andrey1970AppleLife. As you can see, Comet Lake values are really badly capped half the way.

File mirror: 487281_CPUFriendDataProvider-RKL.zip