I am 6'3 295
I think you would be happiest in a jackson karma. It has the most volume, tallest cockpit, and a plaining hull, displacing more water sooner meaning you sit up higher in the water overall.
when you get into rockered boats like a stomper, jefe, or prijon pure you will find the seat is in the center of the rocker putting you deep in the water letting water overtake your stern behind your back.
it is because the cockpit rim is low here, and thats where the water sits. I hope you can visualize what im saying.
I have paddled them all, and I can say with out a doubt, I can really get after it in the karma. It has the volume to displace the water that guys our size need.
plus its the easiest outfitting and quick to adjust or to get room for your legs to stretch.
the only others I can think of would be a fluid bazooka L or maybe wavesports new recon 90 or pyrahnas new burn xl.
If class 3 and under is what your after the remix xp 10 is a roomy boat with lots of volume. but more of a crossover boat, all others i listed are sutable for class 5 whitewater and are specific whitewater boats
also if you are wide and tall jackson and fluid are good, and if you are tall and narrow pyrahna and wavesport are good.
demo like you said, I'll be up in the PNW in april if you dont find a karma by then!!