So I have an old (maybe late/mid 80s) minn Kota 55B trolling motor with 5 3/4" prop and a new 2016 minn Kota endura c2 30 with a 9" prop. My boat is a 14' flat front Jon boat with 9.9. Which trolling motor is going to work best for me? Not sure if prop size makes a difference or age of the motor. I read about thrust and know that speed most likely will be similar.