I remember doing a trip on mainline DL DCA-ATL some years ago on a football Saturday in September when there was a hurricane bearing down on the Gulf of Mexico, and we flew at 20,000 feet or less the entire way. I don't think we had any service on the flight, but the pilots poured on the gas as we got all the way to ATL in 75 minutes (the usual trip takes at least 82 minutes). It was i the 6 am hour and the flight was 100% full.