Which aircraft did you use?
The reason I ask is because in a test made in another thread (
http://forum.1cpublishing.eu/showthread.php?t=34115) the results shows that the Spitfire in COD is roughly 14% slower than real life.
Since your figures show a 14% speed gauge error, it's tempting to suspect it's accually the speed gauge in the spit thats porked, not necessarily the FM
But it might just be a coincidence
/m