Fuel efficient hp

I'm new to the site and have been reading the forums regarding various power plants pushing the V20. The minimum seems to be a 115 outboard vs a 350 GM with ??? HP. The V20 can be a master of many tasks, however, this is what I would like your opinions on: boating in the Chesapeake with occasional trips offshore (20-25 mi) with several beer bellied buddies on board (and otherwise loaded) would a 115 be sufficient? Would a bracket with a (115) improve the performance? The 350 would handle ANY squall the Chesapeake could throw at the V20 but the additional weight on the rear, fuel consumption, fuel tank(s) size, maintenance, etc. are also considerations.Fuel economy/speed with the occasional power to plow through a squall are important - I'm not looking to pass a 26' Robalo with 350+ HP hanging off the transom. And last, the 3.7 Mercruiser seems to have it's "special qualities" like me , but would a 3.0 4 cyl. I/O be enough grunt given the above? Thanks WT.