strange i7 behaviour

[Amit5155]

i have
i7 8700 non k cpu
16 gb ddr4 ram at 3000mhz dual channel
gtx 1080ti
asus z370 f gaming board
coolermaster ml 120 cooler

i am getting really wierd issues with core speed and temps with my i7 in battlefield 5
when xmp profile is enabled for ram the cpu speed drops to 2650mhz from 4290mhz when game is running and utilization goes above 55%.

When that xmp is disabled and i run it with setting the ram speed to 3000mhz manually the cpu drops from 4290mhz to 3990mhz same with load at 55%, all of this while its peak temp is 74 and avg temps is 68.

While running in xmp i understood the low cpu speed is affecting my fps but even when i disable the xmp and run with manual ram speed i get same fps in which is 85-90 in single player. I ran single player so i can compare results.

why is cpu reducing speed even when its not very hot?
what should i do to stop it and get more performance?

pleasr help