I've got a smaller build: ~170 lbs and 5'11". I had to put in 2" thick foam sections on both sides of the coaming to get any sort of contact with my hips. I initially put a big chunk of 4" thick foam in the rear as a seat back, pushing me to the middle of the coaming. Sitting with your back against the coaming brings the CoG too far aft, in my newbie opinion.

I've since taken the rear rest out, since it kept getting pushed down and pulled off when I'd enter the cockpit. I replaced it with a curved chunk of foam that sits right on the floor slats, pressing up against my butt and lower back. It's comfortable, for the most part, but I'll continue to refine it.

Being new to kayaking, I'm loathe to comment on the Sea Tour 15 EXP's performance. I've had plastic recreational 'yak paddlers comment on how fast and sleek it is, though. Turns like an aircraft carrier, though edging and sweeping further out seems to help with it. Knowing what I'm doing (gotta hit up those paddling classes) might help.