The quality of the down is somewhere around 550. You don't know till you open the pillow. I made a down UQ from a pillow and used 27oz along with 20% overstuff. My UQ weighs in at 38 oz total. Yeah it sucks weight wise, but it sure is warm.
If you don't use grosgrain, you can save a few oz.
My UQ fits just fine under my WBBB. No problems sealing gaps or anything. I use the Leighlo suspension system right now. I use 1/8 shock cord and it pulls up tight.