They may have different recipes but I doubt anyone would recognize difference unless told what is he drinking. And pepsi being noticeably is a very subjective opinion not a fact. I've heard many times how they put ********* of sugar in coca cola but I've never heard anyone talk about how sweet pepsi is. But that of course doesn't mean much. To me coca cola tastes way sweeter but I'm not saying it is.
I've been in Atlanta my whole life. Down here if you ask for Pepsi, you get pepsi'd. On a side note I have been in a diner where a northerner asked the waitress for Pepsi. After being denied his garbage, he demanded to know why they don't serve it. He was quickly put out of the restaurant with the applause of the whole restaurant. Don't ask for Pepsi in the birthplace of Coke.