...I forget who told me this but I had the same question when I was buying my 42" sony plasma. I think the rule was something about 5x the vertical size of the screen. Anyway, this worked out to about 8.5 feet away for optimal viewing of a 42" screen. As I am about 9.5 feet away this was fine. Having lived with it now for several months I can tell you that this distance is absolutely perfect for a 42" screen. Now I should add that the smoother the picture created by the most pixels possible allows for even closer viewing distances. Low reolution sets look better from farther away. In your case, sounds like either 42" or 50" would be fine so it comes down to which set you like better. I've always hated projection TV's of any type, but if you love the sets, you should be fine with either one.