I had a 90 2 stroke on one of my boats and a buddy of mine had a new 90 4 stroke on the same make and length boat as mine . His seemed a lil weaker than my 2 stroke . I will be getting a 4 stoke soon to put on my boat but it'll no doubt be the bigger 115 .
I have another buddy that has a 115 Suzuki on a bigger bay boat . It seems to have lots of power and speed for that big of a boat . It surprised me .
The extra power is great for when you need it and like white boots said you don't have to run wide open all the time .
Go with the larger HP and run the engine slower. With the 90 you will want to keep it wide open. With the 115 you can run it just over1/2 throttle. Those aluminum boats are very heavy. It will last you forever though. Your grand kids will just have to change the motor when they get it handed down to them. Wish I had one.