Hi David,
I have a Starlight Xpress SXVR-H694 and I usually run it at -20C. During the Winter months I sometimes run it at -25C. Of course I have to make sure I have a full set of darks and flats to match whichever temperature I use.
I agree with what Francois said, it is important to run your camera at a temperature that it can easily maintain, so that you do not get too much temperature drift. I find the temperature drifts by a few 10ths of a degree, but no more during my exposures.
Best wishes,
Andy