Altai (Siberia), Tian Shan, Himalayas
It's a not a sleeping bag - it's a house!
I was climbing in the Pamirs (Peak Lenin) in winter 2010 and took the CWM everywhere with me. It performed really well in temperatures between -20-31 Farenheit higher up on the mountain. In -10, though, it was just way too warm, uncomfortably warm. I got the 'regular' length and it was nice and roomy for me (5'7).
I would feel comfortable taking it to the higher evevations of the Himalayas.