Case is kinda cheap and I'd rather get something like a 7870 over the 660 for gaming. Also get 8GB of RAM and put the money you save towards a better case or graphics card.
The Gamma isn't a great case and probably not the sort of thing you want to be using for a $900 build. The Corsair Carbide 300R would be a good option, as would the Phantom 410 or the Fractal Design Define R3 or R4.