You might mave a max HP rating of either 8 or 10 HP. So keep that in mind.
With Merc 2 strokes there isn't much weight difference between the 6-15 hp units, same block I think.
My 3 hp rated electric Minnkota will push my aluminum DB about as fast as my 8 hp Merc without the weight and noise, just less torque.
You get to a certain point with the 8 HP and I don't think more throttle will help go any faster. Just pushes more water and raises the bow more.