I had a Minn Kota Endura Max 55lb thrust on my mariner 4, the lakes I fished and trolled got bigger and my battery one too many times. so I upgraded to a 2.5 tohatsu 4 stroke last year. It worked great, but I did reinforce my mount a little with a bit of wood as I noticed the motor really pulling the back end down.
I had built my own wood floor and had 2 pedestal seats in mine.. with the trolling motor I would say at best I hit 2-3 mph, with the 2.5hp tohatsu I hit maybe 4mph. its walking speed at best.
I've since sold my Mariner 4 and got a 12' SIB. Now I'm looking to sell my 2.5 tohatsu and getting a 15hp Merc lol