always use the same ISO and temperature for the lights, darks and bias. the sensor gain is different at different ISO and you need the gain of the calibration frames to match the lights.
you might as well use the same temperature and ISO for the flats, but technically you don't need to use the same ISO. if for instance you are using a light source for your flats that has some native oscillation frequency, you may find that a high-ISO flat exposure would be so short as to not be evenly illuminated by the light source. in that case you can drop the ISO until the exposure is long enough.
this will complicate matters however as you'll need to do 2 runs in BPP: in the first, use bias and/or flat darks of the same ISO as the flats, in order to create a calibrated master flat. then you do a 2nd run of BPP with the light-matching ISO darks/bias/lights together with the pre-calibrated master flat.
rob
