Check to see that nothing else in your pc is bottlenecking (like HD etc.)
TBH, my GTX660 hardly ever maxes out and it looks fine (I don't really mind about framrates)
Im not gonna have an argument, if films in the US are shot at 24 FPS and they look AWESOME what is the issue with not having 70 fps or even anything above 30fps (unless 3d).
That being said, let me know if you have a soluation