I had the Malossi 62cc kit on it before the pipe...FYI.
So....45 is very possible. But I don't think it'll go any higher than that without re-gearing and a variator. In fact, I KNOW it won't.
I'm pretty happy with 40-45, though. I think Elliot is probably right that I'd have to be 100% sure that the moving parts on the pipe are perfectly aligned. I actually really like the fact that my engine doesn't move at all.