I agree with the above, going from stainless to aluminum is usually a step backward. To make any recommendation you will need to determine the diameter and pitch of your present prop. Then we will need to know the RPM that you achieve at WOT (wide open throttle) and the maximum RPM recommendation for your motor. The proper prop will allow you to achieve the maximum rated RPM at WOT with your average load on board. If you prop too small you risk over-revving the engine. If you prop too large, the engine will be lugging throughout the RPM range.