ha, just read this over on offshore. Check your answer over there. I believe they are saying a 90 amp speedo would be good. If you expect to pull 50 amps i wouldn't get a 60 amp speedo for a boat. Since you will likely be using full throttle a lot, 10 amp head room isn't much.

Can i ask why brushed? Is this stuff you already had? The worst brushless motor would probably be better then the best brushed motor in my opinion.