Don't buy a boat just because you fit in it. Boats also have a weight range. Although this is usually more of a factor for play-boats because it's harder to fine a weight-appropriate play-boat for a tall skinny dude. Believe me, I tried. I'm 6'-5", 36 inseam, 13 foot, 180 lbs.

But about river-running, I've got a large Burn that works great for me and I've got room to spare. It's kind of creeky too.