I found this excerpt somewhat damning when I think of some previous debates regarding german planes:
"A. S. Nikolay Gerasimovich, sometime relatively long ago I was speaking with a pilot—a frontline veteran. Right after the war they flew in captured aircraft. And no matter how hard they tried, they were unable to attain the speeds the Germans had written in their specifications. The shortfall in speed was significant. In the end, they prevailed upon a German, a high-level specialist, and asked him, “Why this shortfall in speed? Are we using the engine’s capability incorrectly?” His response was that they would never achieve the target speed, because the German specifications showed the theoretical speed, and they were attempting to attain that speed on their instruments."
Now I wonder about those charts - I had assumed German data to be accurate now I am not so sure.