Thanks. I have a synthetic, snugpak tactical 3, and I get cold in it at +2c, despite it being rated at -7c comfort level. (tactical 3 is 1.7kg, packed 23cm x 20cm). So I was looking at down because I don't want to increase size or weight, preferably reduce. The rab 900 is approx 1.5kg and 24x45...