[Juha]

Hello, they are all practical.
for 2cm Flak 38 the rate of fire is practical, one usually saw the 220 rpm in books, cyclic or theoretical was IIRC 480 rpm. One usually sees its muzzle velocity as 800 - 900m/sec or 830 m/sec for AP and 900 m/sec for HE round, maybe 990 was for AP40 Composite Rigged special AP round which was rare. I cannot remember its mv right now. Weight is right for action.
For 8,8cm earlier models 15-20 is what one normally sees in books. Around 20 rpm was possible for a good crew a while. I haven't thought that earlier but maybe 15 rpm was for 0 degree or horizontal fire because in Flak 18, 36 and 37 the breech was in ackwardly high position for loading when the barrel was horizontal. In Flak 41 it was clearly lower at that position but the gun was partly designed also for ground fire and was more or less as easy to load at 0 deg as at 90 deg, the price was more complicated carriage. Weight was around 5000kg for the older models and IIRC a bit under 8000kg for Flak 41 but that might have been without the shield, so the numbers look more or less correct to me. Muzzle velocity was IIRC for Flak 36 820 m/sec for HE and 795m/sec for AP but 840 is not far of, even the temperature of powder influence to muzzle velocity. Also the 1020m/sec for Flak 41 sounds right. Ceilings for 88s seemed to me rather teoretical. IIRC the effective ceilng for older 88s was some 8000m and for Flak 41 appr 10 000m. Without doubt the shell could fly higher but those lower ceilings are heights were there is possibility to hit something.

HTH
Juha