No way would I go 200 miles further to avoid Atlanta. Granted it helps if you go through often. The middle lanes or even the HOV is what I use. The above post of Athens, Macon, Columbus is good although it adds 100 miles.
I agree if you are southbound on I-75 that US 27S is a good road, especially if you are going to the west coast of Fla... Columbus, Albany, Perry, Fl as it is mostly divided four lanes.
If at all possible do not hit Atl at rush hour... even stopping and killing some time so you are not spending that time sitting in traffic. Next month I'll be headed south and will hit Atl at 9PM because of a commitment at home that evening. This will let me get to WPB the next afternoon with time to setup before it gets dark.