Re: How much would a Marciano win over Floyd Patterson in 1956 do for his legacy?
I think it'd help a bit.
He'd have a signature win over his succesor; The youngest, most primed, formidable contender.
All of Rocky's signature wins have a common element; They were against fading badasses of the era just before him. Still entirely formidable, still exceptionally dangerous and crafty, but past their best, nonetheless.
Floyd Patterson wouldn't have had their skill or know how, but he'd have been the fastest and most explosive fighter Rocky had ever faced, and probably one of the hardest hitters to boot, with the leaping left hook. Rocky would have actually been the guy with the serious experience advantage, but a distinct disadvantage in most other areas.
I don't hold his retirement against him, but I don't see how one could attempt to say that a W over the young Patterson would be anything but a great boon.