I learned something about my bike, when I did a complete over haul this summer, i ordered a factory rear sprocket for it and recieved a 45 tooth rear sprocket. The sprocket that was on mine(what was left of it), was a 48 tooth sprocket. With the 45 tooth sprocket i´m doing 5000 rpms in 6th gear at 67 miles an hour. Here´s a wild guess, but i´m thinking alot of the argument over top speeds could be over this very thing. By the way i´m ordering a 48 tooth sprocket in the next couple of days, although the bike is ungodly quick right now, I like a smooth and some descent top end.