[LoBiSoMeM]

Sorry, but i think you are wrong.

The numbers you supose to be the combat ceiling (climb rate of 500ft/m??? It's correct???), as i read, are the service ceiling (military or civil) of the aircraft, like Al Schlageter said, maximum climb rate of 100ft/m. In CloD with the Spitfire Mk.IIa i can only reach the MAXIMUM ceiling about 31.000Ft. I can't climb higher.

I think you are suposing that over 30.000ft is the operational ceiling of these WWII fighters of BoB time. I don't think it's correct.

Wikipedia:

"Combat ceiling

Combat ceiling is the highest altitude at which an aircraft is expected to have a given (usually 500 feet per minute) climb.[citation needed]

Alternatively, combat ceiling is defined as the highest altitude at which an airplane can sustain altitude and airspeed during a horizontal maneuver with a given bank angle (usually 15-20°).[citation needed]"

I don't tested this situation in CloD and I don't know the real aircraft numbers about combat ceiling. Maybe it's around 28.000/30.000ft.