If your room has ambient light but not from the sides, those HC gray's aren't going to help that much, so you might be better off with a nice "plus gain" screen - say 1.3 to 1.6, to brighten the image. That won't help though if your ambient light is back where the projector is.
Whatever your room for the Optoma HD33, I offer the same advice - should you be able to pull it off. Darken the walls, ceiling and floor of your room. If you can't do it all, do what you can. But, if you can do nothing else, and can manage to darken the wall your screen is on, that alone will make a real difference. If you have the usual off white ceilings, darken them several shades - They will likely still seem as bright to everyone, since the ceiling will likely still be the brightest surface. That worked in my old great room. I darkened the ceiling several shades, and the result - well less than half the reflected light getting back to the screen. - And no one noticed the ceiling change.
My new theater, with it's black ceiling and dark blue walls and floor, just about any projector now seems bright. The HD33 is plenty bright in all modes but 3D. For 3D the Optoma is the brightest home theater 3D projector I've yet, unless you include the passive glasses using LG CF3D at $15K.
Screen size - the whiter the surroundings, the more lumens, or smaller screen to look good. Still, even in a light walled family room this projector can do a respectable job on a 110" diagonal screen, with modest levels of ambient light, for sports viewing. In my testing room with the side walls turned to light surfaces, it filled my Carada Brilliant White 1.4 gain screen in the testing room, without any effort, in all modes. And was actually almost bright on the 110" diagonal 2.35:1.
3D at the smaller HDTV size when I use the masking is almost reasonably bright. Of course, that size is only about 88" diagonal 16:9. Note, with the limited zoom lens, thinking about going with a cine widescreen isn't practical.