The highest recorded power output from an A4 was 2450 drawbar horsepower when "Mallard" herself was hauling 11 coaches (390 tons tare, 415 tons gross) "up" Stoke Bank at a sustained 80 mph in 1963. O.S. Nock thought this performance superior to Mallard's world record run in 1938. An A4 with the same load on a "good run" would be doing about 50 to 60 mph at the summit of Stoke Bank. On a run on 8 September 1961 "Mallard" had its train travelling at 78 mph.