The O.S. Max .75AX will run well on 12 x 7 or 8 propellers. O.S. suggests such large props as they do because of the severe noise restrictions in Japan, their largest market. The .75AX will run well when turning near 12K RPM or even a bit over. They have peak Hp coming at 15K RPM, which means the peak torque will likely be near 12K RPM or so. If you run the engine there, it will run very well, but a lot louder than if you're running near 10K RPM, where their suggested props will have you running.

Performance and handling will be much better at the higher RPM levels.