Dave,


The altitude is irrelevant!

The RPM will be nearly unchanged as you go further up.
The power output will decline as a function of air density, but the prop's drag will too and by the same percentage.

The result, your engine will sound the same, but will not pull nearly as hard.


The corrected HP for Mexico City's altitude - 7,342 ft., of an MA 10x6 at 14,200 RPM, is actually just 0.69 HP.

I didn't know that, I had always been under the perception that RPM's would be diminished at higher altitudes.