Generally, stick to nice 1.0 gain or higher white surface screens, unless you are buying this projector first, for movies, and only 2nd for games. Then you could favor a high constrast gray - counting on the plentiful lumens to give you the brightness you need, but the HC gray type screen to lower those pesky, too bright "blacks." An HC gray will also help if you have side lighting problems you can't mute.
If you plan to be 3D gaming with your GT750, basically, the same thing - use a white screen. The GT750 uses a standard screen, it does not need a 3D optimized screen - those are normally reserved for systems using passive 3D glasses. If you'd like some additional guidance regarding screens and 3D, check out RonJ's blog, that's a topic he's covering in his initial 3D related blogs.