I am 9 to 10 ft away, and I have a 50" Panny 768p model. (Only the old 37" came in 720p.
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I bought last fall. Now, I would get a 1080p model. Back then, the 768p models were brighter, and had a higher contrast ratio because more pixels for the higher res model means more dead space in between those pixels, which means less lightable area. (If you think about that for a second, it will make sense.)
But they have since improved the brightness and contrast of the 1080p models. A lot of people feel that bright/contrast/colors can be more important than resolution for picture quality, so back then, that's why I went with 768p. But now? I firmly believe that 1080p is the way to go for that size/distance combination.
Plus some of their newer 1080p models supposedly can do a multiple of 24 Hz for the refresh rate.