9.8/9.9 is the largest I could go if I want to be able to use it on the lake that is close to work, as it has a 10 hp engine limit. Yeah, our current boat displaces 1220 lbs and has a really old 3 hp 2-stroke...and it isn't really adequate for "larger water" as we found out in the adventure detailed above...but...it also has a tiny 2 blade propeller and isn't a long shaft, so that 3 hp is very far from efficiently used in the water. I'm guessing that a 5 hp with a 4 blade prop and long shaft would be quite a bit better than that even on a 4500 lb boat. Well, anyway, the engine size won't be what sways my decision one way or the other anyway, it'll be the condition of the hull, sails, and other gear along with the price..just want to get a feel for what people feel would be adequate and whether I should factor in needing to buy a larger engine into the equation when looking at these boats.
Keep in mind that you can sell the 5 if you find it is not enough and find an used 2 stroke 9.X.