I have the sitka kelvin and I will say it's not really impressive in any one category, but is still a decent Insulation layer. I got it on camofire and for the price I paid I'm happy with it. I would never pay full price for it. It is marginally warm, the for is good, the weight an materials are not particularly special. Also I like hoods on my insulation layers, especially if I'm going to use them in the way that you said your were. That said its primaloft and it's good stuff. Personally Ive never shied away from down, especially for winter climbing in snow. Your body sweat and vapors will compromise the down far before the snow will as long as you practice good methods, IE wearing a shell when needed and properly airing the jacket out after a hike if you do wear it.
My friend is an Ice climbing guide in Alaska and he swears by two lines of puffy coats, feathered friends and Eddie bauer first ascent. They both offer coats in vetting weights so you can dial in just how much insulation your going to need. None of them are going to be the lightest but they are built very well. I have a hand me down FF from him it has the pretex shell and Is awesome.
