Good evening to all!!! I have recently acquired a 14' aluminum fishing boat and I would like to add an electric trolling motor. Boat came with a 1971 7.5hp Mercury but I don't want to rely on this motor for trolling. I would like to add an electric motor for trolling, and as a backup if the Merc expires on the water. Since I have no experience with these electric motors, will you try to help me understand the difference, in performance, between a 35 and a 55 Minn-Kota??