Made a lightning quick DFW I-D connection a couple months ago flying SYD-DFW-SMF in F, even with a checked bag. We arrived at the beginning of the inbound TATL/TPAC bank (at 1pm), so had no wait to see a CBP agent. By the time I got to the carousel, maybe a half dozen others had arrived, and the carousel started within 2-3 minutes. Bag was one of the first off, breezed through customs and TSA, and was at the FL entrance within 20 minutes of walking off the plane.
Of course, I would've likely had a much longer experience had we arrived in the middle of that TATL/TPAC arrival bank. I think I saw the first 77W from LHR pull in as I walked into the FL.