I have two 46ax engines. They both have 12x4 props and both are in the low 12000 for RPM's. The 12x4 is quiet, better torque ( pull or the aircraft) and you can slow the plane down for landings faster. Yeah you don't get the fast blistering air speed that you would get with the 11x6 but I like the torque and the ability to slow the plane down for landings much better.