Ok thank you for the information
I guess the whole problem here is I do not have a minimum value for Zout - is there any ways to have an idea, based on temperature or like?
Also when I read your message I am starting to think that maybe I misunderstood what the overshoot is: for me it is just the fact that a bit before the cut frequency the gain goes positive - e.g. here as you said getting a gain of 1.17 around 22k. Is that correctly understood or is there more to it?
No, there is a lot more to it.
Overshoot is a "time domain" effect where the filter output, when displayed on an oscilloscope and in response to a step input, initially exceeds the expected final value before falling back to the final settled value. The output level may oscillate several times above and below the desired level before finally settling to the steady value. The amount of overshoot is defined as the maximum height of the peak, in percent of the desired output value, above the final settled value.
For example, if we start with 0V on the input of your filter and then apply a 1V step, the filter output will start increasing until it reaches a peak of 1.17V after about 24us. The initial overshoot is thus 17%. After this initial peak the output will then start decreasing again until it reaches a minimum of 0.97V at about 48us. This is an undershoot of 3%. The output of the filter will continue to oscillate up and down, at decreasing amplitude, until it finally settles at its desired value of 1V. The oscillation of the output before it settles to a final value is called "ringing".
As you are using this filter on the output of a DAC the effect of this ringing is that you can't be sure that you are seeing the correct DAC output value until the ringing has died away sufficiently to have negligible effect on the measured output voltage. The time for this ringing to die away is called "settling time" and a poorly designed filter can extend this settling time excessively. In the case of your filter design the settling time is around 100us before you can be sure you are seeing the correct output voltage within the accuracy of your 12-bit DAC.
You can explore all these aspects of the filter time domain performance by doing a transient analysis in a SPICE program.
With the filter frequency response the rise in gain before roll-off is called "peaking". The "frequency domain" response of a filter can be used to predict the time domain performance of a filter but this requires some complex maths. As a general rule though the presence of peaking on the frequency response indicates that there will be significant ringing on the filter output in response to a step input. The larger the peaking of the frequency response the larger the amplitude of ringing will be and the settling time will be longer.
The converse does not necessarily apply as the absence of peaking in the frequency domain does not guarantee he absence of ringing in the time domain. For example, a Butterworth response filter has no peaking in the frequency domain but still has a small amount of ringing in the time domain.
Again you can explore these aspects of the frequency domain performance of the filter and link them to the time domain performance by simulating the circuit in SPICE. All the figures I have quoted above are from an LTSpice simulation using the nominal component values with your "worst-case estimate" of the DAC output resistance of 6k. The performance will only get worse when you add in effects of component tolerances or allow for more variation in the DAC output resistance.