Have you sat in either a Z or a Crossfire? It is always a good to try these things out yourself and go for a test drive. I'm 6"3 with 211 pounds, athletic and I never had any issues. It "fits" me perfectly. I don't feel claustrophobic and I actually enjoy sitting in the seat a lot more than some higher end sports cars that are too tight of a spot for me.
Btw, I don't own a roadster but the coupe and like I said never had a problem with the space or seats!