Which is better? 12x6 prop pulling 11,100rpm or 13x6 prop at 8,900rpm? My OS 56 alpha is spec for both. OS website specs 1.0hp at 10,000rpm and practical rpm range 2,400rpm to 13,000rpm. Using it on a Fliton Votec 351. Plane seems to be faster with the 12x6prop (but that could be my imagination cos its noisier too). But its so cool flying with the 13x6, I can see more trail of smoke from the plane! Comments appreciated.