Mobo: The Sabertooth is very expensive, but doesn't offer a whole lot of features. The P7P55D-E Pro above has the same main features and includes USB 3/SATA III support for $10 less.
RAM: Faster sticks, probably for less.
HDD: Much, much faster.
GPU: Easily the best single GPU cards out there. This would be able to play every game at max details at 1920x1080 resolutions.
If the $920 is absolutely firm, make these changes: