We too have a 10ft rib, with a 5hp 2 stroke engine and have been cruising for 2 years.My biggest regret is in NOT getting a bigger outboard. We thought 5hp would be fine for getting to shore as it is in the Chesapeake but in the islands, your boat is home and the dinghy
is the car and you often go miles in one to hit the reefs or go fishing and friends with 10+hp would go 3-4 times as fast as us and that is a BIG difference.
So...if islands are your destination and your budget can stand it I would recommend the largest 2 cycle you can handle. Best...GB