I made my transfer just fine, and unlike poor Henry, my plane left on time (10 min late I think).

I arrived at the B "bus gates", so that's probably kind of a worst case and the plane to ATL left from F-8 (end of F terminal). The passport line was reasonable. All lines ("short connection", "normal" and "elite/first class") were about the same length. The security at the gate was short (5-10 people long?). I made my transfer in maybe 30 minutes and arrived at the gate before boarding started. I probably helped a bit that my plane came in 10 min early. 10 min late (20 min later total) and it would have been more hectic. I did not run, just walk quickly.

(boarding was kind of chaotic I felt. the gate are was very cramped and the person checking boarding passes at the plane had a different idea of what rows should board compared to the announcement. But well... that's not related to the transfer time)