I have a Stewart Cine-W 133" Studiotek130 in a batcave for use with my Schneider 1.33x M lens. I'd stick with Studiotek material vs. grayhawk - I don't have any cross-reflection that I'm aware of; I also thought the grayhawk was for rooms with ambient light, but don't know for sure.
In terms of the curvature, I guess I couldn't tell you what I have - I bought my lens and screen from a local dealer and simply told them the PJ and throw so they sent whatever was recommended for it. I'd talk to Stewart (or via your dealer) and see what is recommended. My throw is ~14' 2"... I'll look around and see if the curvature is printed on the schematics.
Very happy with the screen, though!