Consider where you fish and how much running you do. Boat speed might be negatively affected by the extra weight of a second battery if you go with the 70#. If you're not dragging your boat through shallow water all day, the 55# should do the job. If you don't mind losing a little speed for better TM performance, add a second battery and go with a bigger TM. Good point on the charging of the batteries...it'll be a pain to have to remove both batteries for charging at the end of each day. Either way, I'd go Maxuum over the Edge for better speed control. For the length, you know where you fish. If it's important to have a lot of motor in the water, then go with the longer shaft.