I'm not surprised you saw the differences that you did. The blade profile of the Robbe is wider and probably pitched closer to its advertised pitch much like APC. I've often encountered very different rpm figures when comparing MAS to APC. I will say that MAS props are more durable, but they're known for having more blade flex, make more noise, and the actual pitch being a bit less than advertised. Not nitpicking here, just making observations and repeating what others have said. Nonetheless, the Fox ABC .46 makes respectable power which is good to know since I have a new one sitting in its box in my engine cabinet. It's a shame it didn't have the spinner with it - just the spinner backplate.
Personally, I like to know what kind of power the engine can produce (open exhaust) and then try to find an exhaust system that will allow the engine to run close or better than that power figure. Then again, I currently only run my engines on boats so I'm not confined to the same restraints aircraft are limited by/to. Some engines I have will never fly or be run on boats which are the examples I'll run "for the heck of it" on days I have time to burn.