How hot is your CPU getting in-game? I have about the same set-up (8350 + 770) and experienced the same sort of inconsistent performance, however I discovered that my CPU was running way too hot (averaging 75+ celcius ingame) , and after getting a new CPU cooler the problem was more or less fixed. However, if you're certain that temps aren't an issue, could you at least tell me the games you are running?