I also use the APC 9x3 combat, but only my Webras, and only when they are getting up on the pipe and putting out enough power to keep the rpm up in the turns. On my OS's I use the MAS isntead. I find that the MAS 9x4 just pulls through the turns better, even if it does flex a little. Now, with the Webras, when they are turning up, the MAS is just not designed to handle that RPM, so I use the APC. However, at least one of my Webra's is getting tired, and doesn't always rev up (depends on the weather mostly). During the morning test flights, I try it on the APC 9x3combat. If it doesn't perform, I put on the MAS 9x4, which does allow the engine to spin up in to it's power band.

I should also note that prop selection does depend at least some on the airframe, envrionment, fuel, and flying style. What works best for one guy might not be best for another.