the screen is the single most important end of a carpc, it's really all you see in normal use, & it is most of your interaction & control, as well as feedback...
in a sense, the screen IS the carpc... I'd rather have a killer screen with a few comprimises in the rest of the system than a crappy screen with a killer system, of course, best is to have it all, but the screen should take the highest priority as far as I'm concerned...
a killer large screen will be expensive, but well worth it
any frontend will work on a big screen, but sometimes, with extra screen realestate, you'll want to modify the skin to better suit, I mean with a large screen you can have more info available at the same time, & large buttons on a 7" can be too large on a 12.1, so the best thing to really get the most out of it, is to choose a frontend that you can alter to better suit.... but any frontend will work...