Check your CPU temperature, looks like it may be overheating and thermal throttling.
the max temperature is around 60 even in rendering .i use xspc water cooling custom.my problems is that its frequency drops down to 799mhz at ramdom even ifs full load
How are you observing this?
1) Try updating your motherboard BIOS, then
2) Click "XMP" and save those settings
I'm aware that power management is still on. I just want to know if this works properly.
*If you still have problems, try changing the CPU MINIMUM Power to 100% in Power Management. That's not guaranteed to work though as it's a slightly different feature.
I've frankly never seen this issue.