I haven't had any experience with cypress. I looked at the Steam bending instruction Book I got from Lee Valley and they only list hardwood bend radius's. They say softwoods don't bend well and should be avoided. I would expect that most softwoods will probably relax or distort more over time than hardwood. The info I got from LeeValley is on their web site if you want to check the info I've been using. You may also want to check Harvey Golden's site, he has a lot of info on building and I consider him one of the best authorities on Skin on Frame boats.

http://home.pacifier.com/~qayaq/

http://www.leevalley.com/home/main.asp