As a follow on: I agree with Cuban8, supersonic or transonic Mach no.s should be avoided.
If your problem is not being able to absorb enough power within the constraints of a propeller diameter, the answer would probably be more blades.
If the overspeed is because you have optimized the pitch for level flight and powered dives are causing the overspeed, then some kind of pitch control may help.
This need not be as complicated as you think, some time ago I met a chap who sold his own design of wooden propeller at Avra Valley airport in Arizona, he called it the 'almost constant speed' propeller. I believe the trick was to use the aerodynamic twisting moment to increase the pitch as the loading increased by having an airfoil section where the centre of pressure is forward of the torsional neutral axis.
Sadly the designer of this died a few years ago and I don't know of any technical reports, but food for thought anyway.