Yes, it looks like GM's current short box is 5'8", the standard box is 6'6", and the long box is 8'.
Of all the combinations, the only one I think looks really bad is the short box on the crew cab.
And it's funny you should ask this now. I just spent the last two weeks driving a diesel, crew-cab F250 with an 8' box. I never loaded it down with anything more than a couple of duffle bags, so never got to test out its utility, but every time I walked up to it in the parking lot, I couldn't help but think to myself "man, that's one perfectly proportioned truck."
