Thank you for the response.
I have set the swash plate servos to 200 Hz and they work fine so far.
As a tail servo the Blue Bird BMS-22HV was not holding well at 200 or 333 Hz.
Therefor my question for 250 Hz to run them in spec.
The servo never got hot during all the trials.
I tried to tweek gyro gain, rudder delay and rudder dynamic, but the best case was a 2-3 mm wobbeling per side of the tail with a low frequency. With the best adjustment I changed to a Align DS455 tail servo and everything was perfect.
One idea from a friend is still open:
What happens, if the Blue Bird servo runs on 50Hz. Some Savöx typs have to be on such a low frequency.
Just last trial for a low-budget tail servo.