I tested these in my works walk in freezer where the temp is -4F and I was super hot even doing little or no work. They are so full of high quality down and are reinforced with thicker material around the knees and but. The overalls were a bit big so I had them altered with extra Velcro higher up so they fit on my waist better. I sized up to a large so they could easily be placed over my shells for Mountaineering. Can't wait to try these out in some serious cold weather. Not only did they come with a stuff sack but also a storage sack. Nice work Marmot! Perhaps on the 2010 model they will have more options to tighten the waist a little more to keep the warm air in.
A year later (3/29/2011) I called Marmot and asked for the down fill weight of their 8000M Collection, this is what I was told:
8000m Pant - 296grams / 10.44 oz
8000m Parka - 504grams / 17.77 oz
8000m Suit - 692grams / 24.4oz