So I'm going w/ a group of friends into the Adirondacks in February. Last year it got down to -20 degrees F. I understand that 800 Fill is better than 650 Fill down given the same weight...but, as I view the many down jackets available I am having trouble figuring out which coats are warmer than others. For instance:

The Marmot Zeus Jacket is 1 lb. 1 oz. w/ 800 fill down:
http://www.backcountrygear.com/catalog/appareldetail.cfm/MA4208

Then u have the Mountain Hardware Sub Zero Jack @ 1 lbs, 11 oz w/ 650-Fill Power 85/15 Goose down:
http://www.basegear.com/mountain-hardwear-subzero-jacket-down-sale.html

The Zeus is lighter, but higher fill down...the Sub Zero is more weight (more down?) but lower quality down (does the 85/15 mean ratio of down to feathers? Thus even less warmth for the weight?) and it ~looks~ fuller and warmer.

How am I supposed to know which is warmer? How do I know one jacket doesn't just have extremely heavy zippers (:p) as opposed to more ounces of down to keep me warm?

Please forgive my newbie knowledge...I guess I gotta learn somewhere.
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