Another Trolling motor question

I have a 17.5 Duracraft all weld boat that came with a 12v MinnKota
44/AT trolling motor. It is a five speed motor and I use it on "4" all
the time because "3" is about like watching paint dry and "5" is too
fast generally. The boat and 50 hp Yamaha and all equipment weighs
less than 1000 lbs I imagine.

I would like to get to "3" being my most of the time speed. I am
trying to decide between a MinnKota Maxxum 55 12v and a MinnKota Maxxum
70 24v. The difference in price is about $100, plus $300 for a two
bank charger and two new batteries at around $100 each.

So, it will cost me an extra $500 on top of the $569 for the 55# thrust
motor.

I hate to go up to a 24v motor, but don't want to end up with a 55 that
is not noticeable better than the 44 I already have.

Anybody out there using the Minn Kota 55 edge or maxxum? If so, what
kind of boat and are you satisfied with it?

Any other thoughts?