They are a warm boot and LS rates them so. I have no issues at around zero degrees though I don't believe that they would be all that warm past the -10 degree threshold.
I also have owned the Spantiks and boy were they a dream to have. They were very warm and climbed extremely well. However, I found that in the CONUS, their weight and warmth are unwarranted and thus found the Baturas more suitable to climb in while I am in the states.
I cannot speak for the Scarpa Cumbres, but I feel that you'll be very happy with the Batura (http://www.moosejaw.com/moosejaw/shop/p ... GoogleBase). It's warm, has a nice toebox and hikes extremely well. You may also want to look at the Scarpa Phantoms for a comprable boot: http://www.zappos.com/scarpa-phantom-guide-orange
