I've been looking at getting the Big Agnes Storm King bag. I'll be using it for 3-season backpacking in MT and CO (high altitude with potentially cold nights). I already have an insulated air core pad which I like better than a regular thermarest. The reason I'm looking at the BA bags is because I ALWAYS slide of my sleeping pad and loose whatever pillow I have in the process. I haven't found a lot of substantial reviews on BA bags, especially ones that comment on how they perform in cold weather and I was hoping some people here would have some good input for me. About the only I have read on the BA bags is that they're about 15 degrees off on their ratings, which is I why I was going for the 0 degree bag and planning on only getting 15 out of it.
Thanks in advance!

reviews...http://www.backpackgeartest.org/reviews/Sleep%20Gear/Sleeping%20Bags/

No real experience with them, myself. I considered the system briefly and moved on to lighter, more compact gear. I like to bundle up in whatever I'm sleeping in. Didn't look conducive to that.

Haven't actually used or seen one but one thing I read that I would never have thought of. Because the pad slides into a sleeve one can't sit up in one. It's too stiff. Just a thought.

Sitting up is one problem the other is bending your legs if you sleep on your side. I had a Zirkle and sold it to a guy that sleeps on his back without tossing and turning.

Really a good idea if it works for you.