All these data are from real life data original documents.
As you see chart is original from flight test for SPit MK1 ( 100 octan) then i put there speed chart for Hurricane MK1 +12 lbs also from real life test ( spitfireperformacne site) and data for 109 E-3 is from original German manual ( best score i have seen for 109 E at 1.45 Ata ( 1 minute emergency power) - 0 -500 km/h, 570 km/h at 5 km).
All is here in these topic - it is enough to read it carefully
http://forum.1cpublishing.eu/showthread.php?t=20110