You should post this in the "Extream Speed Prop Plane" forum. A lot of the talk is about normal fast airplanes but if you look around over there you can get info on the World record holders in Europe. However, the engine you have is a far cry from what the speed speed guys are using but you could break 100 mph on a Q-500 type plane.

I just realized you have been in the speed forum. There is some good info there but you may have to search for it.