Just finished a low water trip with 4 boats - a 16' raft, two 14' rafts, and my 16' cat. The 16' raft was by FAR the best boat for the conditions, which sort of defied conventional logic and forever altered my thinking.
Because of the heavy sedimentation (everywhere - not just at the bottom stretch), there are many rocks and sandbars that sit just a tiny bit below the surface of the water. Assuming you're carrying a load (which you of course will be), the bigger boat just rides higher and sits more on top of the water instead of scraping. Other than in Government Rapid, my cat, which can usually get into places where rafts can't, was clearly the worst. Loaded, I had 9" - 11" of the 24" tubes submerged, and I had to pull and push more than anybody.
BTW, is bgarnick Brady, by any chance?