This will probably sound rude. I do apologize.
I don't think you know what your looking for, or at least you aren't communicating it very well.
A down jacket has pretty much one purpose. It is that extra insulating layer to give you more warmth. Compare it to fleece or another synthetic jacket that is solely for insulation.
With a layering system, you generally have 3 layers. The first is the next to skin layer, think long johns. The next layer is an insulating layer. This can be one piece or many, depending on the seasons and expected temps. The last layer is the wind/waterproof layer.
The last layer doesn't insulate, and the inner layers aren't waterproof. If the jacket has the name "shell" in it, then it is most likely an outer layer. This is the gortex stuff, or eVent or other types of waterproof/breathable. I would say the most durable are made from canvas and coated with oil to make them waterproof.
So, my question is, are you looking for an insulating layer, or an outer shell?