APC 12-4 -- it will give you entirely adequate airspeed, better climb than the 11-6 & slow you down very well. As you already said, the 12-6 is too big -- much too big. Whatever you use, you want to reduce the pitch, but reducing the pitch means increasing the diameter to keep the correct engine load . Assuming that the engine is idling as slowly as is reliable, you want to cut the propeller idle-speed discharge velocity, but maintain the correct load on the engine. ----- APC 12-4.