Don't have any experience with a down sweater but I just purchased a pair of Montbell down pants to use as an insulation layer. They are about 5 oz. and performed great this weekend. I used them over SW long johns and had nylon hiking pants on top and was toasty warm in camp. It was very wet from raining all day so no campfire and in the low 40's/upper 30's. I also used them as a pillow since they were too warm to sleep in.

I get quite cold in camp and sleeping but I think I could get 10 degrees out of the pants...and plan to wear them in my sleeping bag to extend it's rating so I can go out year round. (mid-TN winters anyway!)

Millette