LazyHas there ever been a fix for this? I have a 7850. My fps never dips below 60 but I'm feeling some extreme choppiness at random times when I'm moving my mouse. Seems pretty random but it doesn't usually happen immediately after starting TF2. Easily replicable on tr_walkway by letting the bots run for a few minutes. I've tried updating graphics drivers, changing mat_queue_mode, disabling aero, setting a max fps but nothing really helps.
Yeah as #26 said it sounds like your CPU is either overheating or simply not good enough to run the game anymore, I've got a 7850 too and I haven't had any problems like that.