Check out the Mamba and the Diesel for sure. Those two boats are fast and surf very well. The Mamba has more of a peak to the top deck and will shed water a little better than the Diesel. (Auto resurface on big drops) I think that the Diesel front surfs better, and the Mamba spins a little easier. Both boats make kayaking easier in general. The difference for you might be comfort and outfitting, and only sitting in the boats will tell you which you'll like for those long days on the Rio.
Really either boat will be great, and both will do the job.
I love to dance, but who needs the music- It throws me off.