In reply to nickinscottishmountains:
I'd also disagree about the fit. I've got wide feet and have had various pairs of Scarpas down the years and agree they do seem to fit wider feet quite well BUT I've a pair of the original Nepal Extremes (from 2000) and they're the best fitting mountain boots I've ever had. I've also got old Trango S (2001), OK fit on the forefoot where I'm wide, a bit funny round the ankles and Trango Extremes (circa 2006) which are a bit narrow on the forefoot but 7 odd winter seasons in them have sort of battered them into an OK-ish fit! I also got Sportiva Baruntses a year and a bit ago and they're also ok-ish forefoot fit although pushed on my little toes, but with thermofit inners I sorted that out. So I know people say Sportivas fit narrow, but it's not all the models all the seasons. I think though I have a narrow-ish heel and ankle, so it maybe that if you are wide there as well, their heel cups might be too tight.
OP - I've saw someone with the Rebel Ultras last weekend. It was about -12 and he said he could feel it more than with his old boots, although I don't know what those were. I think if you're moving a lot you can get away with pretty light boots if they fit well. But stand for 2 hours in deep damp snow belaying your mate in classic Scottish misery conditions, and I'll bet you'll get cold feet in them!