After getting samples of the Stewart Firehawk G4, Stewart Cima Tiburon & Screen Innovations Slate, I went with the Cima Tiburon. My room has pretty decent light control but does have a light colored ceiling. Screen is on the smallish size, though: 100" diagonal. I realize it won't have the ambient light rejection of the G4 or Slate, but by far it had the most uniform, smooth surface.
Going into the selection process, I already knew what I didn't want: Sparkles, grain or anything showing up in large light colored areas of the picture. My previous screen, a Da-lite Cinema Vision had this in spades - and it drove me crazy!!
The funny thing is when looking at the samples: although the gain of the Tiburon is rated at .95, and the G4 at 1.1 and the Slate at 1.2 - the Tiburon looked brighter than both of them. I'll report on it when I put it up in about a week or so. Cine4home had a really great review of the Cima Tiburon on their site.