Yep, I had a really interesting few hours with Rab's Neil Mcadie the other week talking about bags, ratings, construction and yes, the outer fabrics too. If you missed our preview of the new bags, the lighter the fabric, the easier it is for the down to loft, so the more efficient it is, but... coated fabrics like Endurance actually make the bag slightly warmer because there's less heat loss through the outer shell.
The down side to that, apart from a slight weight penalty, is that a bag with an Endurance outer needs airing properly after every night's use to allow trapped moisture to evaporate whereas a bag with, say, a Quantum outer is inherently more breathable and allows vapour to escape during use, so only needs occasional airing.
New range does look very, very nice and clearly a lot of research and thought has gone into the construction and design of the latest bags.