I'm. Also in the market for a new tiller, and the yammy is my choice hands down. A little more money, but they are the best in all aspects IMO.
My hunting partner. Has a new 40 yammy on his lund, and its a sweeeeeet engine. I gotta get me one.
I'm getting 32mph with a 96 2 stroke. Mariner 40 right now.....on a wide body 16 ft starcraft....my buddies new 4 stroke can't keep up, and his boat is not quite as wide, and I would think a bit lighter too.
I don't think you'll find much top end change going up 10hp, but you will notice more bottom end for sure.
The new yammies with the electronic throttle controls are wicked quiet and sooo smooth.
S.