Cayo... let me clarify on the whitewater. First, I ran it at definitely low flows. I would say the ratings are accurate and the funny thing is that in my guide book the authors portaged a lot of the major rapids after detailing how dangerous it would be if something went wrong. I agree that if you were to lose a boat or get injured, you're screwed. However, for paddlers of strong intermediate/expert abilities, it would be at least as dangerous to portage 6 days worth of gear and a heavy boat on the broken shorelines. The guide book authors were using open canoes as opposed to my Journey. So, even though the ratings are accurate, there are only four class III rapids, and one easier class IV in 84 miles.... a fair bit of I-II, but mostly Gore style flatwater. Hence the Journey. I think a ducky would be a horrible idea. You need the fastest boat possible. It's definitely mostly flatwater with the potential for upstream winds.
All that being said, I had regular 80 degree days just before christmas! It's an awesome adventure if you need something to keep you sane in the off-season.
Here's the Texas first D: Bear Creek
Mostly a joke really, but I do have something legit up my sleeve if it ever rains again...