I have seen the Clostermann and 45min quote several times in several sources though that is not definitive.
Pierre Clostermann (Free French) wrote of the Tempest:
Nothing was left undone to give the Tempest a maximum performance at medium and low altitudes. Special auxiliary tanks were designed even, with perspex connecting pipes, to fit under the wings. Quite extraordinary attention was paid to the rivetting, the joints and the surface polish. The result was a superb combat machine.
It had a thoroughbred look and, in spite of the big radiator which gave it an angry and wilful appearance, it was astonishingly slender. It was very heavy, all of seven tons. Thanks to its 2,400 h.p. engine it had a considerable margin of excess power and its acceleration was phenomenal. It was pretty tricky to fly, but its performance more than made up for it: at 3,000 feet, at economical cruising on one third power (950 h.p.) with two 45-gallon auxiliary tanks, 310 m.p.h. on the clock, i.e. a true air speed of 320 m.p.h.; at fast cruising speed, at half power (1,425 h.p.) without auxiliary tanks, 350 m.p.h. on the clock, i.e. a true air speed of nearly 400 m.p.h.; Maximum speed straight and level with + 13 boost and 3,850 revs.: 430 m.p.h. on the clock, i.e. a true airspeed of 440 m.p.h.
In late 1944, the Do 335A-1 superseded the A-0 on the production line. This was the initial production model, similar to the A-0 but with the uprated DB603E-1 engines and two underwing hard points for additional bombs or drop tanks. Delivery commenced in January 1945. Capable of a maximum speed of 474 mph at 21,325 ft with MW 50 boost, or 426 mph without boost, and able to climb to 26,250 ft in only 14.5 minutes, the Do 335A-1 could easily outpace any Allied fighters it encountered. It could also carry a bomb load of 1100 lb for 900 miles.