Good stuff, thanks guys. Here's my sitting position with the backrest fully inflated. Feet are kinda jammed in there. Moreso with my hiking boots (though it sounds like this might be a good thing?) I wonder if it would get uncomfortable sitting like this for a few hours without being able to stretch my legs. I guess I could always put my legs outside the boat on calmer sections.
With the backrest deflated i get a little more room, but I'm not sure I'd want to paddle with the backrest deflated.