65-70C seems a little hot. That may explain the stutter you are having.
Record your temps, on both GPU and CPU, while at full load(while gaming).
Also, that card isn't good for gaming at 1080p resolutions.
Regarding the video card, I beg to differ; every game, for the past year, I was able to run at 1080p on a 5770. Except for Metro 2033, which was way better at 1600x1050.
But indeed, the CPU temps are a bit high.