CPU Multiplier intermitantly dropping

[lynd25]

I have a water cooled kraken x52 i7 8700k set in the BIOS as all core multiplier 50 and voltage in offset mode at 120mV.
Stress testing in windows kept below 70C.
However in OSX High Sierra HW Monitor, CPU multiplier keeps dropping from x50 to x 8 on idle. Is this normal ?
Haven't changed any setting on my install. Do I need to configure power somehow?

 

[Adam.Smith]

I've seen that on stock settings on the 8700k in high sierra. I just installed osx on saturday. I figured it's for power/heat saving. But it ramps up when I'm gaming.