Hi, I had the sunsport 270 V airdeck rated for 8hp,,,,, started with a late 70s yam 6hp was in good nick. Would only plane with my self in.
Then got a 80s merc 9.8,,,,, changed the boat 100%
. A fraction over rated on paper,,, 9.8 at the time will have been calculated at the crank and not at the prop as now. Plane with me, wife and daughter in. Then got hold of a late merc 15hp,,,,
. Well over rated,,, but good fun.
A 7.5 or 8hp will make a difference from your 4hp. Once on the plane you can drop the revs down and probably use less fuel than the 4hp at WOT.
It can get addictive, now have a 380 aerotec use either the merc 15hp or Johnson 30hp.