I know of a Ranger 23 owner who used a 4 hp 2 stroke outboard for many cruises in the Peconic Bay estuaries and did fine even with the current there. He could also anchor and then put the 4 hp on his dink. I'm not Rx'ing the 4 hp. Just giving a reference point. At some point the extra weight on the transom is a negative. And keep in mind the transom may not be built for the heavier more powerful engines - especially 4 stroke vs. 2 stroke.
When racing my 26' keel boat, the Ranger 23's, Ranger 26 , Beneteau 23 & C&C's 25 would remove the outboards and put them on a cradle in the cabin. That's what we thought of weight on the transom.