While the .25FX could probibly fly it, you won't like it. You'll be at full power most all the time, and acrobatics (even a simple loop) will be really hard to do. And you'll need to make all kinds of noise to do it, since you're going to need to wind the motor up to some serious RPM numbers. Totally not worth the effort.

However, if you do try it, a 9x4 prop is going to be the way to go. I'm running some OS .25 FX's in my combat planes. 9x4 MAS prop, mousse can muffler, 19k+ rpm isn't out of the question. Great for roaring around chasing other planes, but not great for a trainer.

Oh, it also depends on how high you are from sea level. If you are a couple thousand feet up, forget it. Being closer to sea level will help. So will colder, denser air. Summer in Denver would be right out.