48 MPH would be acceptable and a HUGE improvement over the factory setting. With my current tire/wheel setup, I'm able to hit 41 MPH, however, it's all but impossible to maintain that speed since I'm constantly bouncing off the rev limiter.
I am really only considering this modification for the times I use my P520 on the street. I just want to be able to cruise at a consistent, and honest 45MPH on the street and not completely stress the machine.
Mike