Sorry but I can't agree, a larger motor uses less amps to get from A to B.
Sure both running at 100% the smaller motor will will use less amps over a set time but the bigger motor would've covered a hell of a lot more ground.
If you wish to troll or work along a bank casting lures at say 2kph the smaller motor will be running a lot harder and be using a lot more power from the bat to achieve the same result. Working harder it will also run a little hotter and that also uses more amps. Throw in an adverse wind or current and the difference in the amount of amps used is magnified again. In all brands of elec motor the larger sizes are also technically more economical to run.
In saying all that I'm sure you would be very pleased with a 55 or abouts and just get the biggest battery you can fit in your boat, 130 amphr is good and will go for a couple of days without running flat, running flat will f##k up your battery.
OH and the auto-pilot function is fantastic.
Starting to see quite a lot of Snakes with probs about 6 to 12 months out of warranty, some have taken over 2 months for parts. I would pay more for the Minn kota myself cause if I was away somewhere like Awoonga and I had a prob, I could get the part overnighted and and be fishing again later the next day.(It happened)
Salt or fresh? If you're only fishing the saltonce or twice a year I'd go with the freshwater model and use some Inox before and after each trip in the salt.
Cheers
Mike