Had many lightweight down jackets but the best I have ever owned in terms of warmth and lightweight is the Eddie Bauer Evertherm. It is breakthrough design and has received many awards. If you have not seen it check it out. They even make a waterproof (yes water proof) version that is also one of the lightest waterproof down jackets.
I’ve got the Men’s Nanopuff and it’s great for being synthetic but I use the Outdoor Research Filament jacket more because it’s warmer and lighter and still water resistant. Since we should be carrying waterproof/windproof shells I’m hoping for the Ghost Whisperer without the hood. It’s been on my radar for awhile and I’m dying to try it out.
SotoLibre
I have the Nano Puff jacket without the hood and it's a great jacket. I take it everywhere.