In reply to andrewm1000:
> Any suggestions on 1) overboots and 2) insulated gaiters (supergaiters) for extra warmth with my very comfortable Nepal Evos.
Super gaiters - even the insulated ones don't add much insulation to your foot because most of the heats is lost through the sole. This at least is what 'the books' claim - but my personal experience is the same. Supergaiters do keep your laces from freezing up and snow from starting to melt in the creases of your boots etc. and that does help keep your feet warmer particularly if you are camping and don't get chance to dry your boots.
Two Easters ago we were climbing in Arctic Norway in pretty brutal weather - 10 to -15 probably but next to open sea and windy and my feet were OK in Nepal Extremes with uninsulated Extremities super gaiters, but we were retreating to a hotel each evening. I've camped in that area before in winter and used plastic boots with Yeti Extremes and was fine that way. But might you want to consider getting warmer boots to start off with, before going down the overboot path?