I currently have a 46lb Motorguide on my 16 footer. I had a Motorguide on my last boat and have been pleased with both of thems. I will be going to a 56 when it is replaced. If you have a 55 now and want more power both when it is new and down the road, it seems like the 74 would be your best bet. All motors that I am aware of above 55 lb are 24 volt.

Best of Luck,
Bumblebee