If your room has ambient light but not from the sides, rather straight back, 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. Some HC gray screens are better at rejecting light coming from above, than others.
Whatever your room for the Acer H9500BD, I offer all, the same advice:
Should you be able to pull it off, darken your walls and ceiling, and if possible, also the floor of your room, to dramatically improve your experience. Keep in mind with a bright projector like this Epson, however, you can cut through quite a bit of ambient light when you want to watch sports, regardless of walls... 2000 lumens can go a long way.
If you can't really redo the room, 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, you can, as I did, 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.
In m y new theater, with its black ceiling and dark blue walls and floor, just about any projector now seems bright. The H9500BD is downright brilliant, and is the first 3D capable home projector in here for review that is actually fairly bright on 3D on screens over 100". Wow!
Even the testing room with about half of its wall surfaces set to off-white, the projector easily handles my 110" screen (2.35) when filling the full width with a widescreen movie in 3D.
Most likely you should chose a white surface with gain up to 1.5 for this Epson, or a high contrast gray surface, if your layout benefits from it.