I'm currently using my Saito 45S in a low wing model - sort of like an Astro Hog - wingspan about 52". Our field is about 100' above sea level.

Running a 10.5 x 6 APC on 10% nitro/17% coolpower/3% castor mix. From memory, it turns about 10,800 on the ground. I'm not a believer in extracting the the very last drop of horsepower from my engines, so possibly you could get a couple more hundred RPM than me. If I want more power, I use a bigger engine.

I did try a 12 x 6 MA but it was too much of a load for the engine on that particular model. An 11 x 6 APC was better than the MA, but the engine appears very happy with the 10.5 x 6 APC.