I'd get the BIGGEST one you can afford!!! At the Minimum 50", but I'd be looking at least 58" or larger. Really, You can't go to big. I went from a 42" CRT Rear Projection HDTV to a 50" Plasma. The TV is further back as it takes a lot less room being so much thiner. I also have my components Under it instead of on the side of my HDTV so it's really taking up less space now with the larger HDTV!!! I'm just under 7 feet from my display.
A larger display, the picture is larger and so you can see everything even better. Sports, see the Football better when it's thrown as it's larger. You notice more. It's either get the bigger TV or sit closer. Bigger TV, you can sit further back, have a larger group of people around if you want. With a Plasma, the viewing angle is HUGE, even way off on the side of the screen the picture is clear, not so with a Rear Projection display where directly in front is the sweet spot!
Because screen size is measured Diagonally, a 50" SDTV is going to be larger then a 50" HDTV Height wise, though width would be wider. So watching a 4:3 program on the HDTV would give you a smaller picture. So you have to up UP in size to equal the same height. Also because HDTV's have a much higher Resolution, you can go much larger for the same distance anyway then a SDTV. On a SDTV you needed to sit far enough back to not see the pixels on the screen. Larger the screen the worse it would get and the further you had to get back. On a HDTV, if you sit to far back from to small a screen, your not going to be able to see a difference with Blu-Ray over a DVD. So go BIG.
