i run i5 @ 4.5 (liquidcooled) with a gtx 670 lightboost 120hz.
i still have frame trouble every now and then. it'll differ per map as well...and when steam community goes down or magically comes back
This game is picky. I can stream csgo @720 no problem. 300+fps. tf2 i have to stream 960x540 to not get frame fucked. It's not even the frame loss sometimes with streaming, it's the fact it doesn't feel like 120hz anymore. but i digress... some little things that may mess with your game
steam community overlay
mumble overlay
running windowed vs full screen
if you have very low ram
if your hard drive is almost full
having message notifications pop up on your overlay
other processor/memory heavy applications you may have running in the background
trial and error. in any case, i highly recommend overclocking. the improvement is definitely noticeable