I wanted to offer a few observations and some solid info on DWR light fabrics and weights. It is extremely rare than a fabrics ID number, .8, 1.1, etc, is what it really weighs. The industry standard is to name it for the uncoated or untreated weight. So, the familiar 1.1 silnylon is closer to 1.35 and a .85 DWR nylon is about .95-1.0.
Another factor in light fabrics (light nylons, silk , etc) for sleeping bags or clothes is that a lighter fabric can always be used but it may pass air too quickly and then you have to use more insulation for the same temp rating.
For a while I used a .8 DWR (really .9) in the pursuit of lighter and lighter and since I've switched exclusively to the Momentum 90 DWR from thru-hiker.com(about 1.05) I've seen a big difference in the warmth, fabric strength and DWR quality.
So, the small weight gain in the fabric results in a net gain for the temp rating, DWR effectiveness and the amount of insulation needed (possibly less).
FYI on the Momentum 90, the outside is flat black for speedy drying and the insisde is heat calendared for downproofness. It's awesome stuff for bags, clothes and bivies. A bivy from it may weight .5oz or more than a .8 (.9) fabric (ex. Pertex Quantum at 30gm/sq/m or about .9) bivy, but it's a good trade-off in DWR protection and strength.
Along the same lines, a 1.1 or a 1.3 DWR may not have as good a DWR as a lighter fabric.