Hi Lems, I'm currently on an APC 12,5x11 at about 10.500 rpm maxed out on the ground. Webra reports I should get 10.200 with their pipe and 10% fuel but they are conservative and besides I use the Hatori 700. I'm gonna try a 13x11 next to get the revs down. I use 15% nitro and 15% synth oil. RPM should be below 11.000 rpm and I'm sure it revs up to 11.000 in the air on that prop that's why I'm going for the 13x11 to see. The prop noise is a bit much and I too have problems with the MK mount - it's too rigid for the Webra! I got the OS 91 FS mount which has rock hard rubber. I should have gone with OS 61 mount which probably is a bit softer.