In reply to Jamie Simpson - Alpine Dragons:
I've used Scarpa Phantom Guides and Ultras, as well as some old Raichle All Degree XP (I think).
The Ultras seem the closest fit and most minimal, so probably the least warm, but they're also the lightest, so that's probably to be expected. I think they're really good and would be happy to wear them to reasonably below-freezing conditions, and to recommend them generally - they seem to have come down in price quite a lot this year, too, for some reason.
I don't recall any particular instances of cold feet in any of these boots (worryingly numb toes, hot aches etc) - but I suppose it's hard to have a properly objective assessment of them since other variables can have such an influence on one's warmth.
I've not had the Ultras long enough to comment on longevity, I'm afraid, but the sole unit is thinner than on the Guides, so I suppose they'd be bound to wear down more quickly with lots of walking-in or use on rock.
My Raichles have done pretty well, apart from the crampon welts getting a bit mangled - but you can't buy them now so that's by the by.