I have both a dedicated theater room with the JVC RS-1 1080p projector and a family room with the Pioneer Kuro 150FD (1080p plasma.) The primary seating area in the family room is 15' away from the plasma and I daily regret not having a larger screen. The farthest seating area (I have three rows) in the theater room is 22 feet away from a 108" screen and that row is the least desirable view. What I have learned in my experience is that bigger is much better and that 1080p only allows you to sit closer and have a larger screen. The best view in my house is the first row in the theater room, which is 14' away from the screen.
Good luck
Good luck