This week I had a 12x7APC, 11x6Evolution, and 12x6MAS prop on my 55AX. It's still working it's way into making more power and the 12x7 was too much load for it (10%nitro). The others worked very well, and I found the 12x6 to be the best combination of speed and pull. I'm hoping a 12x7 will be just right after another few gallons and the engine is making max power.

It all depends on what you like for that plane. Give a few props a shot.