Seven pounds isn't horrible when you look at the cost of the Colman. Lighter, stronger, cheaper- pick the one you need and the one you want, becuase you aren't getting all three.

When bags are rated, it is an unwriten rule that they are assuming you have on a proper base layer. (Maybe it is written, I've just never found it.) At 10, that means socks and a beanie, long johns and something around your torso at -10. It is only one and two season bags that they figure you are going to sleeping in your skivies in. If you aren't properly dressed, you need reduce the effectiveness of the bag. They are also expecting you to have it on a pad suitable for the weather.

Who's making a waterproof bag? You can get gortex bivy bags and such, that go outside your sleeping bag, but I can't think of single reason why you'd want one below zero. You want to be able to get your water vapor OUT of the bag, even if that means you are loosing X amount of calories, if the bag gets wet, you'll be loosing about 4X calories on the first night, and pooched every night after that until you have a chance to let it air out some place warm for a week or so. Once down gets wet, it is a major pain in the butt.

Others have answered the question about fill pretty well.