Montaniero

Hi There, I would like to start by telling you that I have regularly been checking the posts in CC and found them extremely useful. There seems to be a lot of experienced people around here and is for this reason that I would like to pose you with my current dilemma: I am interested in buying a 0º F (-18º C) degree down sleeping bag for winter mountaineering and alpine climbing. I am looking for: - The highest fill-quality (800+ or 900 fill power, if there is anything like 900-fill in the world!). - Lightweight (important for alpine climbing) - Great Design/Construction I've already rounded my decision on either the Marmot Lithium or the Marmot Couloir DryLoft, both on sale at Backcountry Store. I already have a Marmot bag (CWM, -40º F) intended for expedition use and I only have great things to say about it. I have not tried any of these two 0º F bags and would not be able to do so as I am not in the US, but design is same as CWM and that fits me perfectly (5'10", 160 lbs.). Design and construction wise, these two bags are very similar. They mostly differ in the materials used. This is my pros & cons analysis so far: MARMOT LITHIUM Insulation: 900 Fill Goose Down Fill Weight: 27oz / 767g Shell: Pertex Quantum N-090 Ripstop Lining: Pertex Quantum N-090 Taffeta Total Weight: 2lb 8 ozs / 1133 g Half Zip PROS: - Lighter by 1 lbs. (important for alpine). - Higher 900 Fill-power (is this for real?!?). MARMOT COULOIR DRYLOFT Insulation: 800 Fill Goose Down Fill Weight: 30oz / 852g Shell: TwiLight DryLoft® N-143R DWR finish Lining: Gossamer Micro N-130R WR finish Total Weight: 3lb 8 ozs / 1590 g Full Zip PROS: - More water-resistant (DryLoft instead of Quantum, important for alpine). - Full Zip instead of Half (I guess is not really an issue in the cold temperatures this bag is intended for, specially using a pee bottle). Which one would you choose? I would appreciate the input of any people knowledgeable with these two bags. At the end of the day and supposing both bags are equally warm, it's a matter of the lower weight of the Lithium vs. the more water-repellancy of the Couloir, right? Many thanks. P.S.: Although the differential on the fill weights (27 vs. 30 oz.) tricks me in terms of both being equally warm. I guess it correlates with the fact that with the higher 900-fill you can have the same temperature rating with 3 oz. less down. Can this be correct?