Gray screens are good with dealing in rooms with (white) reflective walls since gray screen reduce reflections that white screens and walls can cause. If you are using black, non-reflective, dedicated home theater room, white screens, neutral (1.0) gain screen are the best choice because of reduced reflections. Since you are using it in a room with white walls, I'd encourage the ReAct II Gray screen especially since that screen has a higher gain (1.2) than the white screen (1.0), and thus is even brighter, although it's viewing angles is smaller.
The AE7000 is an definite improvement in brightness over it's previous projectors, not quite in league with JVC or Epson, but it can light screens in many home theater environments regardless.
If you want, you can also output your HTPC in a Cinemascope aspect ratio (say 1920x816) with your video card drivers or Powerstrip, which either option, it's possible to present. It's worth a look.