Also check out the DIY section of this forum, there is a user who is doing black screens for high ambient light rejection and it looks pretty decent. LG has a high end laser projector that uses a black screen too for ambient light viewing, so apparently the idea gets tossed around.
Personally I think daytime viewing should be done on a TV, leave the projector for night time viewing. But if I was absolutely set on it, I'd definitely spray paint a screen black or do a DIY grey on black spandex setup, with a high lumen projector. The BenQ HC1200 is also something you may want to consider.