No such thing as to much power, especially in TM's. Will you need it all the time, no. However, windy days, surprise storms, or just getting around the electric only lake all power is useful. Instead of running a smaller motor at a higher setting which runs batteries down quicker you can get the same speed at a lower setting. And you still the extra in reserve for when you need to hustle it a little.
Get the largest one you can buy and have battery space for.