1. Get a map of ATL and know where the gates are. The various concourses T, A, B, C D and E intersect an undergound train at a perpendicular angle. If your gate is close to the intersection, good. If not, you are in for a long walk. This is the biggest factor IMHO than the disance between say A and E.

2. Many departures are delayed at ATL. So don't give up, even if you don't think you can make it--your departure may be delayed and you may get there before it departs.