I use a 3 1/2 Tohatsu 2 stroke that weighs about 36lbs. Pushes my Brig 9 1/2 foot RIB just fine and gets me to and from the mooring and out exploring new anchorages great.
Last summer while anchoring at Cuttyhunk in the Elizabeths I saw a fellow try to get his 8 HP outboard from his dingy to his Trawler. He and the motor ended up in the drink. Lost his engine in 10' of salt water and mud. Cured me from wanting something more powerful.