If you've got the ground clearance, you could even try a 12x4 on the 46 AX. With a trainer, you'll get lots of thrust to get off the runway quickly. Also, think about using an APC prop. I maidened a Tower Trainer with an OS LA 46 Monday for another club member. He was using the provided Nylon 11X5 prop, and takeoffs were long and iffy off our grass field. We swapped it for an APC 11X5, which apparently has a different air foil, and performance went up markedly. It turned about 300 rpm faster, but more importantly, it was up off the grass in about half the distance.

Brad