VNANUS:

Horsepower ratings on model engines are utterly meaningless. They are rated at some RPM like 16000. No real world sport engine with a propeller on it will turn anywhere near that.

And that's assuming that they don't just make them up in the first place. (Why not, nobody can prove them wrong since the engine won't turn 16000.)

You should be concerned at how fast each engine will turn a 12.25 x 3.75 APC, and the only way you are going to find that out is though the experience of others in your club and on forums like this or honest comparisons like Clarence Lee does in RCM.

For your info, the experience of the guys in my club is that the Magnum 52 will turn a prop a little faster that the OS 46AX, but the OS is much easier to tune and your changes of getting a bad one are much higher with the Magnum.

Jim