Think in the end it will come down to Romney winning above the Mason Dixon line and Perry below it.
Cain will strip votes away from both Romney and Perry.
Rick Perry may not have the strength to win much in the South during the primaries either. He makes himself look worse with every debate appearance. Rick Perry is doing poorly in Florida right now, and he's not doing that well in South Carolina. If he doesn't win at least one of those states, his campaign may never recover.
Any Republican should win most of the South during the general election.