Don't you have a 40hp on it now? You won't over power it wiith a 40/28hp or a 60/40 for that matter. As long as it's legal in your state and you can get it insured it wouldn't bother me to put a 50/35 on it. If your boat has much more then a small deck, trolling motor and a couple seats I think you'll be under powered with a 25hp. The 25hp would probably push the boat but if you get a big load( fully decked, couple batteries, trolling motor, couple guys and tackle and the kitchen sink :lol: ) you'll have trouble getting up on plane with it.