I heard Blood Mountain is good. If you check google maps, its a bit far away from Atlanta. From what I've seen, its worth the trip. When I get home later this year (9 more months, can't wait), that is on my list of things to do.
I'm just East of the perimeter. Blood mountain and some other roads nearby there in the mountains can be very gratifying rides.
I will say that they get damned busy though. Even on not so perfect days, the main stretch up blood mountain can be absolutely jam packed, with many bikes regularly breaking double yellows at speed to pass, which can make it seem hectic for everyone. There is also a single decreasing radius turn on there that just eats bikes heading up the mountain (I watched an ultra classic eat it there, last time I rode it).
I might also still be replacing plastics from the last time I was up there (although my off was a lot less dramatic).
Still, it's definitely something to check out and the surrounding area is really neat. I love going up that way in the fall time. lot's of tree covered mountain roads.