Just a few more thoughts.....

Generally I'm not into trolling but at times it's what seems to put fish in the boat so I do it. It was almost impossible to slow the boat down enought to get my baits down deep enough to be effective. Any of the infinate variable speeds will be easier on the batteries than any straight 5 speed from my understanding.
My current TM is a MG Tour 55# 12v. Could I use more thrust somedays? Sure I guess so but I have to say if I had to do it all over again, I would go back to the same set up. I tried my 70# TM at full speed once...I thought it was going to rip itself off the front of the boat and it was super hard to controll. I did have to put bolts with fender washers on them as the regular TM expansion type plugs simply pulled out of the alum. I also asked my self, if it were that windy would I even stay and fight it or would I move to look for calmer waters anyway. Most times I would move. If I had a really really heavy glass boat, I could see it. As far as aluminums go, no way. Bigger ain't always better.
One thing I like about my 12v with 2 batteries is if my starting battery gives up the ghost from running all the electronics, livewell, bilge and lights, I can pull one of my TM batteries and use it as the main battery and keep on fishing. I've never had a problem with going all day on my set up. My set up re charges fully over night so no problems there.

Glad I could be of some help.