The 496HO's are suppose to run under 5200 max. It will hit 5000 when i'm by myself and low on fuel. If I labbed the props I think it would be close to the 5200 limit. I'm told the HP drops off above 5200 on the 496's. I don't know what the peak RPM of the 500's are suppose to be, do you ever hit the rev-limiters?