I have a 40" 1080p TV with an HTPC connected to it. The text and icon sizes can be adjusted, regardless of your resolution. The biggest problem you may encounter is if you plan on using the HTPC to view websites. Even though the text size can be increased, the html frame size on some sites don't scale with the text. I think you'd be fine with a 50" screen size, however, so my suggestion is to go 1080p if you can. Of course, you can always run at 720p with a 1080p TV if you feel the need, but the reverse isn't true.