A higher pitch will lower the rpm but it may cause overheating by taxing the engine or other components too much, at least that's my understanding of electrics, I'm sure there's some latitude there. What you really need to do and if I were in your shoes is find out what the recommended rpm is for the motor? That would be the place to start and work from there. Maybe you could send an email to the company with your questions, I've done so in the past and most are more than willing to respond.