Thank you Rick,
I am always keen to learn new tricks and will certainly need to investigate whether I can measure bias drift in my little camera
I have checked single frames with the method from the link you provided, and these are noise estimates (biweight midvariance) I got:
Single un-calibrated sub: 0.9828
MB and Flat calibrated: 0.9842
SB and Flat calibrated: 0.9851
I am assuming the smaller the number the better, so these results also indicate that I would be better off with Master Bias (and possibly could add more bias frames to it, as well as it probably would not hurt to take a few more dozens of flats).
EDIT: Possibly a silly question...in PI, would overscan only apply to calibrating Bias frames (BatchPreProcessing Script)? And can I collect new bias frames with overscan enabled and use them to calibrate Lights and Flats that were captured without overscan enabled?