1) I tried to use this guide, but I’m not sure if it worked or not. Intel Power Gadget and AppleIntelInfo show different frequencies, but neither system.log nor console messages have any evidences mentioned in this guide. Moreover I have "kernel_task" process that takes much RAM and sometimes I experience serious hangs. For example if I want to resize a 9000x5000 image to something smaller the entire system hangs for 30-45 seconds. Internet says that "kernel_task" may slow down CPU in case it is overheated, so probably OSX sees the wrong temperature? The fixes offered by Internet assume disabling PM at all, but this doesn't help in my case. I assume something is wrong with PM.
Generally this machine works slower with graphics processing tasks than my laptop (see signature), though on paper it should be faster.
2) OSX: 10.12.3
MB: Asrock H61M-vg3
BIOS: 1.90
CPU: i5-2500K
GPU: GTX 950
3) The guide is a little inconsistent so the things I’ve done are:
a) Set iMac 12,2 in SMBIOS
b) Downloaded ssdtPRGen from the BETA branch, executed it and installed SSDT.aml into EFI/Clover/ACPI/Patched
c) Unchecked generating of all states and don’t drop any of OEM tables