Maybe this map should be the final arbiter. It includes those areas:
>
> http://en.wikipedia.org/wiki/File:Pin-pen.svg
And omit central Virginia's horse country? No way! That might even stop south of Richmond, a (if not the) definitively Southern city; I can't tell by eyeballing it.
If I were going to base an answer on linguistics alone, I'd sooner go with the map above that one at your second link:
http://en.wikipedia.org/wiki/File:SouthernEnglishMap.jpg
But it's a question involving multiple cultural factors, as well as economic, political, and historical ones.
-- "Hige sceal þe heardra, heorte þe cenre, mod sceal þe mare, þe ure mægen lytlað."
