I don't mean to jack the thread, but the question has pretty much been answered already. More or less everyone here will say that 5" feels fine. Not amazing, not mindblowing, but fine.
I read on the about.com sexuality page the other day that average length is between 5.1 and 5.7 inches while average girth is 3.5-3.7. I find that very hard to believe in terms of girth but hey, that means I have a monster cock hahaha