I think top speed isn't relevant, just 0-40. But one little story, I was being chased by a queer (I mean quad), and I got wfo in 5th. That was first of all way to fast, and second, I didn't see the rock on the trail that threw me into a wild unstable wheelie. Kinda scared everything out of me. One of my little xr100 friends tried to explain that his stock xr will do 80, and that my 125 will do 130.
One of the things that bugs me the most when you end up in a conversation about top speeds is people tend to guess how fast they're going. I've talked to people on stock geared 500's that swear they reach over 100mph. So I ask, what were you being clocked or something? No, they're just guessing because they were wide open in 5th gear, so it just had to be going at least 100.
Most of the time I can tell people are BS'ing just by finding out what gearing they run.