if your using a 11x6 or 7 on a 40-47 engine your have way to much prop for the engine. While the engine may "turn" it it will not like you and won't give you as much power as you could be having. A lot of people fail to understand that our engines (like all engines) have a torque curve where they make the most power. This is around 12500-14000 on the ground. For most .46 engines a 11x5 will put you in the 13000-13500 range and 10x7 in the 14000 range.