Followup review of the RPM, in light of the newer crop of river runners that are now on the market...
I still think the RPM is a great design, especially if you're into long boat play and slalom-style moves; however, for general river running, it's no longer the best out there. Kayak companies have finally figured out that there's more to creating a river runner than just rebranding last year's playboat design. Examples? Wavesport Diesel and Dagger Mamba. Both are more stable than the RPM and still have most of its other positive traits. The only things you give up are the ability to do stern squirts and a bit of hull speed.
Pros for RPM - good hull speed for it's length, but short enough not to be too hard to maneuver. Low volume stern makes for good front surfs and stern squirts. Easiest rolling boat ever made.
Cons for RPM - low volume stern can catch and flip you in bigger stuff and makes it hard to carry extra gear. This is the best river runner I have ever paddled! I may someday buy a slicy little playboat, but I'll never sell my RPM. You'll hear a lot of folks say to avoid displacement hulls like the plague. If you're planning on learning to playboat, that's probably good advice. But if you like running the river between playspots as much or more than the playing itself, the RPM can't be beat.
The RPM has great hull speed, stability approaching that of a flat hulled boat, and good maneuverability. Boats like the GT and Booster are capable of running rivers, but it's a lot of work. The RPM does so effortlessly. For example, a simple diagonal move across the current takes 3 or 4 times as many strokes in a GT than in an RPM.
Of course, the RPM doesn't sidesurf quite as well as a planing hull boat, but you can't have everything. As a class III river runner, the RPM rocks!