Well since this topic is going off the deep end I want to give my 2 cents worth.

I figure that the engines I power my planes with will unload enough in the air to go way past their top static prop speed. The planes are certainly aerodynamic enough. The hughe carbs on them should allow the engines to go to their limit. And the large props are certainly holding them back while running fullspeed static. So when run full speed level in the air or shallow dive I expect a 6500 static engine to get close to 10,000 rpm.

Assumptions apply to a,

BME115 in a SD Katana
3W56 in a GP Extra

But not to a ZDZ50 in a GP Ultimate---Too much drag