Judging by the quality and performance I am getting out of my 1600mm-c at 0* I don't see the need to run at -25. I don't think it would be achieving very much more. In fact I haven't bothered with Darks yet. Some of my early experiments at ambient were still incredibly clean and free from hotspots or noise. Must be a lucky sensor.
My aim is to standardise probably at -10* now I have most of the basics sorted out. Cooler runs at about 5-10% power and I'll build a darks library soon.