The 11x6 will make the planes' speed easier to manage than if using a 11x8, easier to needle, less chance of running too hot, provide better vertical, better throttle response, etc. Just a better all around sport prop. A 12x5 might pull the plane around better, but would be easier to damage on the runway. I've got a Rossi .45 with a tuned exhaust and it won't turn any 11x6 prop anywhere close to the point of failure......IIRC 15,500 rpm is about all that sucker will deliver.