When I had my first boat (O'Day23) I was using a 9.9 Evenrude 2 stroke I was getting about 1gal. per hr. at full throttle and making about 5kts. Then I switched two a 6hp. Evenrude 2 stroke . I got a little bit better mileage . Both engines were smooth and quite . One good thing about the 6hp. was that it doubled as my dink motor too . I'm not 100% sure but I think if you are buying new, a 2 stroke would be hard to find . I don't have the O'Day anymore but I do have a Tohatsu 4 stroke . It's louder at full throttle than a 2 stroke but quitter at idle . This is just my opinion , I think you would do well 6 hp 4 stroke.