I see. At 12 ft viewing distance, THX recommended screen size 107" (16:9)diagonal. Obviously, the bigger the screen you get, the more interesting the value becomes from FP.
If going RP, and you have more to spend, I would take a hard look at Sony SXRD XBR-2 70". IMO, the Sony's have smoother, better video processing, and just simply look better than most dlps. The issue is that Sony is dropping RP altogether to concentrate on LCD's where profit margins are better. The fact they are pulling out of RP is a sad thing for the value-minded, size-minded videophile. I think msrp is about 5k, maybe you can find good discount, if you can find one at all.
At 14" PJ mounting, you can go very big indeed. But at 12ft viewing, your screen should be of the "modest" proportion.