Will,
Matte white screens are ideal in completely light controlled rooms. With a 1272Q and that size screen, I wouldn't go below 1.5 gain. Above that, you get some hot spotting and color shifting. Some people are really sensitive to it, others don't seem to care. Depends on how much old academy black and white stuff you watch. If you don't watch any B&W, you could get away with a higher gain screen. Higher gain screens also work better in non-light controlled rooms.
I used a 2.2 gain screen with my 1272Q and was able to get over 11 ft-lamberts at peak white after a lot of tweaking. Plenty bright. With a 1.5 gain screen, you'll be around 8, a little low but OK. With a 1.1 gain screen, you'll be under 6. Not bright enough unless you go with the next smaller screen size.
Right now, I'm using a Sony G-70 with a Stewart Studiotek 130 1.3 gain matte white screen. I wouldn't go back to a high gain screen.
I'm sure there's a happy medium for you around 1.5 to 1.8 gain. Or a smaller screen.
You might try posting in the screens forum to see what other folks have to say. This is a fascinating and somewhat controversial subject.