Stewart's booth had a 1/2 grey 1/2 1.3 gain comparison and an identical projector beside it shooting onto a full greyhawk. Yes the blacks are much improved, on the 1/2 and 1/2 you could tell that the whites also suffered a bit. However when you looked over the full greyhawk on the left you couldn't tell that the white level was lower, however you could clearly see the increased contrast. A little trick that your brain pulls called brightness constancy explains why the white on the greyhawk appears just as bright. The greyhawk also performed much better under ambient light, they had a lamp there for comparison.
Unless you're really pushing the size of your screen and you need the extra brightness (i.e. if you're right around 12 ft-lamberts with a 1.3 gain), a Greyhawk would work very well for you.
Regards,
Kam Fung
