I would personally start out on an 11X5 which will give nice pull but not allot of speed and will give good braking for landing. When you are comfortable then slowly increase the pitch while leaving the 11 inch diameter say move to a 11X6 and if you want more speed then go to a 11X7.

Remember that will larger pitch, there will be less braking for landing and also do not go to large on the pitch and it can actually start to load the engine to much and slow the plane down while overheating the engine.