3Putter,
I remember a conversation from the early 1990's about gas formulations with an engineer from the Valero refinery (Mapco at the time). He said that most, but not all, of the Memphis gasoline was made at Mapco with additives blended in to spec per tanker. He went on to say that Exxon barged their fuel to Memphis and did not buy any from Mapco. From your post it sounds like that has changed. Also IIRC, Conoco at one time had a terminal in Lucy, although I'm not sure what products they unloaded there.
As far as marketing hype vs. vehicle performance, I'd say let your wallet and your observations be your guide. My wife swore up and down that her Volvo 240 required Amoco Ultimate to start and run properly. I thought she was just wasting her money, but hey her car. I filled up her car one day to be nice, but used Amoco regular. I was busted shortly thereafter.