I have an Alsek. Unlike other bags I have had (WM Summerlight, ...), the down stays in place nicely. It is filled sufficiently that the down doesn't fall to the sides. All the other bags that I have had now seem underfilled in comparison. I did not order any overfill on the Alsek and I don't think it needs it down to the stated 22F temperature.
The shell is Pertex Quantum, which is very light and silky and has good windproofness and DWR. The same fabric is used in the North Face Verto windshirt, as well as a lot of bivy tops. I find a bivy unnecessary under my full coverage tarp since there are no drafts with the pad attachment system and the shell fabric already has excellent DWR.
I have no experience with Tim's quilts, but honestly the Alsek is just about the nicest piece of gear I own and has the rare distinction that I cannot think of a single way to improve it. There is nothing I would change about it. That is the definition of 5 stars for me.