mmm, i am not shore what to do. I unfortunately cant go the 1000 watt motor because of silly legal restrictions where i live. with a 600 watt motor i am worried about insufficient talk so would like to maximize it but i don't want to sacrifice battery life, it is silly to give the motor 40 amps when all it needs is 20. I will be using 3 12v 17 ah agm(sla) batts btw. I am thinking you may have swayed me and at first i will go a smaller controller and then mby get the kelly later if the first melts or just does not have enough talk.