ORIGINAL: KWJ48
I use a 13x4w and a 12.25x3.75 on my katana profile. I like the 12.25x3.75 better.
I've tried both of these sizes in my Reactor, although the 13x4 I used was a Pro Zinger. The 12.25x3.75W APC definitely has a lot more thrust, so that is what I am currently using. Unlike the 120AX, the 55AX has its peak power at high rpm, so to get maximum thrust you want a relatively small prop.
My Reactor really likes to tip over on takeoff/landing so using the 13x4 wood prop would also get expensive.
Malcolm