Don't forget that it's really about torso/neck/head length and not just overall height that matters with respect to headroom. I'm 5'9" but I have a long torso/short legs (which comes in handy for, well, nothing
) and I just clear the roof of my GT with a helmet on, while my friend is 6'2" with "normal" proportions and has at least the same clearance with a helmet on in the same car.
Al