I had a 9.5 Johnson on my 1648 alumacraft. I hated it. It's like a barge just pushing through the water, since then I have rigged a 40hp tiller handle on it and now it is a real boat.
I have a 1648 w/ 40hp 2 stroke. Boat is completely rigged for bowfishing. Four batteries all the bowfishing gear and I am getting right at 31 mph with three people