I'm using an i7-8700K in an ASUS Prime Z-370-A mainboard and it clocks to 4974MHz. stable.
All I did was to set my multiplier to 49.0, and my Bus Speed to 101.51, and the RAM is at 1624.7MHz. per memory bank. (dual channel 3249.4MHz.)
I am using a 240mm AIO to cool the CPU. My temps stay between 34C and 68C depending on load.
Sounds like you need to invest in a better CPU cooler.
Last edited by RealNeil; 02-12-2019 at 08:25 PM.