ORIGINAL: DenverJayhawk
I'm using a 14x6 and 14x8 on my OS 95AX and it only turns a little over 9k RPM. I'd guess a 14'' prop might be a little large for the 75AX.
The OS .75 AX instructions call for a 13x8, 13x10, 14x6, 14x8, or 15x7 size props. My .75 AX turns a MA 14x6 prop at 10,000 rpm.
Bruce