Scott, it seems that your Luke's Ultralight link leads to this thread.
The Borah vest is the lightest, as you mentioned, but it also lacks a collar. I find that a collar has a big effect on the warmth of a vest or jacket, particularly if it is windy. If you decide to pay for the BRG vest, be familiar with the material options. The "7DS" is silnylon. I have misgivings about using silnylon for the outer shell of a down vest. The Luke's Ultralight vest seems like a good option. It has a puffy collar and a full zip. Also, keep in mind that Ben at Goosefeet would probably make you a vest at a price between the LU and BRG vests that has box baffles (plus the other standard features: 10D fabric, a puffy collar, and water resistant down). It would be as light as the others but warmer.
