-- Last Updated: Jun-22-13 11:19 PM EST --
Your boats are slow because they are short, not because they are wide. The extra width is a very minor concern compared to what happens if your speed gets up within roughly 0.8 mph (for boats of that length) of the theoretical maximum, and for your 10-foot boats that's about 4.7 mph. Most recreational paddlers go about 3 mph or less, and at such speeds the effort will be pretty minor in any boat. Once some people "turn pro", they really lose sight of the fact that tubby rec boats actually require hardly any effort at all going at speeds of about 3 mph (FAR less effort to paddle them than the average canoe, yet no one says canoes are too much work to paddle). Still, you'll really feel the difference when carrying a load of camping gear so it might be a good idea to do a trial run sometime with that amount of weight on board, just so you know what to expect. Of much more concern than speed is your tolerance for sitting in the boat for four or five hours. If you have no practice doing that, do it soon, at some location where you can quit early if necessary (not on an isolated river) before finalizing your trip plans.
On the other hand, the comments about gear storage are spot-on. If you have experience and the right gear to "go ultra-light", it's a very do-able trip. If you can't keep gear volume to a minimum, it may be advisable to get different boats, or maybe just rent a canoe this time. In any case, make sure you have good waterproof storage for everything (real dry bags or industrial-strength plastic bags, NOT trash bags). If you have an accident on the water you don't want to be out in the middle of nowhere with wet clothes and a wet sleeping bag.
By the way, back in the days when I camped on the river, I used a 12-foot jon boat propelled by useless 6-foot oars, and back then I didn't know enough to minimize my gear load so the boat was awfully sluggish. Maybe my tolerance for hard work is better than some, but I found it a very pleasant trip.
Your concern about finding an empty campsite is probably well-founded. I haven't camped on that river since the early 90s, before the preserve and established campsites had been set up. Also, I only camped in the fall when I had the river all to myself. I do know that on any nice summer weekend it's a very crowded river, but it seems to me that the simple solution is to be ready to hit the water EARLY on your first day. If you are on the water about three hours earlier than the rental boaters, you should have your pick of campsites even if you travel more slowly than they do. I'd recommend doing that even for a day trip. That river is SO beautiful, but much of that will be lost if you get stuck among crowds of rental boaters who can't keep from running into each other and feel the need to constantly shout everything they say.
EZ Launch™ Kayak & Canoe
Recreational Kayak Paddle
Paddler's Truck Rack