Since thread was drifting I decided to make an arbitrary split to keep some focus. Also changed the title of the original to better reflect the content. Art Fiedler's comments are very interesting and make me curious into what these changes were that made this bird more effective.
A factory fresh and fully equipped P-39 must have been impressive to pilots used to Spartan wartime produced early to mid war Soviets Soviet types. However the Soviets did catch up by the latter half in all areas that mattered to them.
IIRC American deliveries were mainly factory fresh, British deliveries tended to have been used (sometimes extensively). That must have made an impact on how these a/c were perceived.
Regardless there seems to be a general consensus that American aircraft were regarded as well produced, equipped and even relatively luxurious. From Buccaneer to B-29.
http://forum.12oclockhigh.net/showthread.php?t=12858