After I had made this post my buddy Daniel Harro asked I add this:
"Here is a Marmot Helium 15 degree down sleeping bag after spending three nights on Peak 11,300 in less than ideal conditions. Two things that helped get the down soaked..... 1. Their is no way to stay dry climbing through waist deep / chest deep snow for three-four days, if you were not getting wet from the snow you were sweating from the huge effort of moving upward. 2. these bags are nylon which have no water resiliency what so ever so any snow / water that touched the bags they simply absorbed. Over all a great learning experience!"
Eric Williams back at Mountain House base camp. Harro photo
Couple of thoughts come to mind on staying warm. Climbing in a wet snow storm all day will get you wet if you are dressed wrong. Or being over dressing for the conditions will get you wet from perspiration.
I've used my synthetic parka to dry my soft shell out in wet snow conditions after I got chilled on a belay. I couldn't get myself dried while stopped without added insulation. I also have used a base layer to do the approach in, knowing I would soak it and then changed to dry clothing to do the climb. That is a lighter and much warmer tactic over all for me.
The major issue of winter climbing is moisture management. Be it boots, clothing or sleeping bags. The reason it is an issue from what I have seen is people over dress for the activity level, just as likely use the wrong piece of kit or simply don't pay attention to the details like getting into a down bag with wet clothing on. Current soft shell technology in a snow storm (done it myself) is not the smart option. Doesn't matter what it is made of, wet gear is a poor insulator. You stay warm by staying dry and hydrated.
There are climbs I wouldn't take a down bag on and climbs I wouldn't take anything but a down bag on. It depends on the amount of care I can/want to dedicate to the bag and amount of space in my pack.
Some times a very light synthetic over bag is a good answer for keeping your down bag dry and being able to dry your gear at night. Put the wet gear between your down bag and the liner. But climbing into a down bag with all your wet clothing on is a sure way to soak your down bag no matter what high tech shell material the manufacturer used to keep it dry. Climb "cold" so you aren't sweating and have less clothing to dry at night. Use Synthetic insulation in bags and jackets where appropriate. Staying dry and warm is a thinking man's game that should be played 24/7 in the mtns.