Because of the physics of hull speed, there is no benefit to a motor over 2hp unless you are trying to get up on a plane. Your costco dinghy is a planing boat,

Because of the physics of hull speed, there is no benefit to a motor over 2hp unless you are trying to get up on a plane. Your costco dinghy is a planing boat, and is designed to take a ton of power so it can still get up on a plane with a few people aboard. The smallest 2hp outboard is equal to about four strong men rowing constantly that never get tired... any boat under about 18 feet long will be able to do hull speed upwind in any wind that wouldn't immediately sink or flip it with just 2hp (or really, even with just 0.5hp if this existed). In a small raft that isn't planing, more than 2hp won't get you anywhere faster, under any conditions. There is a lot of benefit to the smaller motor- it will use a lot less fuel, and can weigh under 20lbs. Especially if you go air cooled and/or 2-stroke... combine the two and it could be as light as ~10lbs. Less weight on the transom makes a small boat substantially more stable and controllable in rough seas.