You will seldom ( unless very cheap boat ) blow through the transom hp rating. My 12 ft john boat can take up to 15 hp and I have a 8 and I think 15 would lift me damn near off the water. My 20 ft has a 150 but it is papered up to 200 and really needs a 175 at the minimum. Many dealers keep cost down on new hulls by under powering them and folks a 115 on a 20 ft hull is not a good match. Oh it will work but load it up fishing and you will wallow. That said your to much hp is a bit unfounded. Thing is just because you have 50 hp in reserve on the throttle does not mean you have to use it but you have it when you want it.

Also look to balance your hull. If your going 4 stroke you need to count pounds and where they are on the hull. PNW aluminum boats are not known as performance hulls and the average boat is transom heavy. Sturdy & reliable but not the best performing. Your dead rise and bow angle will also make or break you. DW's E tec 150 makes him scoot but he does not put it to the wall every time but when he has to get up and move it does and right now.

The final thing is a motor you run at 90% will not last nearly as long ( or breakdown free ) as one running at 75%. That top one third of the power band is where the vast majority of your wear happens so it is always better to have a goodly amount of hp so at a cruise your motor just lopes along.