-- Last Updated: Oct-21-12 11:50 PM EST --
At about 185-190 "dry" weight before gear, I find the Fuse 64 does not have much reserve buoyancy for river running. It is great for surfing. With some rescue gear, spare paddle extra water, I'm probably reaching 210lb at least, and I felt I wanted more buoyancy out of it for river running...
I'm 6'4" with long legs and large feet and I can't even sit in the 56 so no idea how it compares. But for surfing I think the more volume is better and is actually more retentive (would remain in waves holes better) than a smaller volume that would sit even lower in the water.
I'm not much of a playboater but I'm learning. That thing has way too much volume for flat water tricks, but on a wave it is nice and it is fine as a river runner too, as long as you don't want too much speed - compared to something like the Dagger Axiom that I recently got as a second boat along with the Fuse, the Fuse is slow. Compared to shorter playboats, the 64 is fast -;)
The 64 might feel a bit more stable and harder to edge though than ideal, and of course, it is longer and needs a bit bigger waves than the shortest playboats to enjoy best...
Edit: I'm voting for the 64 in terms of volume for your needs at your weight. But fit is important. There are a bunch of other similar designs, Jackson Super Fun or 4Fun are options as is the SuperStar (for even more play). If I could fit in the Project 64, I'd swap my Fuse for one of those for sure - my thinking is that if you got one boat, something like the Fuse or Fun series is great for both river running and some decent play capability, mainly surfing and flat spins. But if you already have a Diesel, that can front-surf pretty good already on longer waves, so why not consider one of the more "forgiving" true playboats, like the Star or Project X series? These can do all the Fuse can do (might need steeper waves) but they also are more playful and can do a few more tricks that you might find desirable down the road. They can still run rivers just fine, as long as you are not looking to go fast or attain upriver much...
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