Actually I do think that the new FM will be closer to reality for high alt but on low altitude it is equally bad or worse for all aircraft.

On low altitude, to my understanding, ALL planes except the Spit 2 were TOO SLOW (the Spit 1, the Hurricanes, the G50 and the 109 talking about fighter alone. Bombers I do not know about). What I see is that apparantly the WEP of the 109 will eventually provide a minor speed increase but that's it. It seems also that WEP altitude range is too large.

So actually they should increase high alt speed for all planes and low and medium alt speed for all planes except the Spit 2 wrt to current FM.

I agree that the performance should be as close to historic values available and when I speak about historic values I speak about reasonable historic values that allow to assume that this value corresponds to an averaged historic value. That is to say that they should not just take the flight test of the best or worst performer of a type but try to find the value that represents the average. I admit it may be difficult to get enough historic data but there are clues.