This speed chart is ETO 1943. The graphs are from
WWII Aircraft Performance. The top speeds of the Messerschmitt twins are from one of William Green's handbooks.
The USAAF bombers came in at 25,000 to 28,000ft. Which of these aircraft would
you like to fly?
The Germans did not have any form of two stage supercharging until they brought out the Junkers Jumo 213 pretty well at the very end of the war.