even still, if the projector can't handle ambient light, the screen won't help that. at least nothing you'd want to do for your intended use. high gain screens are expensive, and still may not get the results you want.
you're better off spending your efforts finding a bright projector or setting up a 'booth' to block light around the screen area.
I'd say you keep projecting on the bare drywall, but spend your effort making sure as little light as possible hits that drywall. put up shades or something to block the light. you can still have enough light in the room, as long as the wall is cast in shadows it will help quite a bit
Displays: Samsung PN64F8500/JVC X35
AVR: Pioneer VSX-1130K, 7.1/5.1.2 audio
Sources: HTPC(Enby), PS3, XBOX360, Wii
Control: Harmony One