I will try to arrange field data on a hp/pound basis, which should be a direct mode for engine power comparison for 3D applications. HP/pound both on plane, and on engine level.
Don't shoot me down yet! Stay with me a moment.
I know there is the torque@rpm and prop noise issue, and hp alone will not do, so I will try to put the engines in rpm or prop diameter ranges for best operation. (larger props fly 3D better)
There also will be the mechanical heat sink and cooling issue, which defines the heat stability of an engine, so different engines can, and will score significant user points in different fields of application.
Finally, there is the plane balance question. Will the plane of your dreams balance with the engine, or will it require a pound of lead in the nose when the lightest engine is used?

At the moment, I have more questions than answers. If you have data, I would appreciate getting them, so I can work out a comparison web page which should facilitate engine choice on above mentioned parameters.