So as of late i'v noticed that my cpu will idle around 3.6-3.8 but can turbo up to 4.4 IN GAME shit gets different it slows down to 2.0 sometimes 1.7 GHz! My thinking is that it is using it's turbo then gets sent to the freq clock.... somehow? dunno but i'll post a vid of it later as evidence
If it's slowing down so much while gaming then it could be a sign of the CPU overheating. Check temperatures.