Here is the document mentioned earlier.
http://www.kurfurst.org/Performance_...catter_web.jpg
13 a/c
4 below spec -5% > 31%
6 below mean > 46%
3 above mean > 23%
The average for all the a/c is well below the mean.
Applying this to the Bf109E would give an average speed of ~485kph.