This has been gone over a few times Reflected and I disagree, we do not have 1939 planes, in some cases they are much worse. Though the Spitfire Mk IIa is giving +12 lbs boost speeds even with +9 lbs boost showing on the guages.
Another link where some of the community are testing the AC performance.
http://forum.1cpublishing.eu/showthread.php?t=20196