Winter sleeping bag recommendations?

I just picked up a FF Vireo, with an extra 4oz in the lower half.  It's a 3/4 bag with no zippers that comes up above my shoulders, and I sleep in my big puffy jacket.  It's light, 1lb4oz and great for 20 degree nights in the cascades.  If you're bringing a puffy jacket along, might as well make it part of your sleep system!

Feathered Friends makes some bags with continuous baffles for the down, so you can shift the bulk of the insulation to the top half of the bag if you have a particularly good sleeping pad. I've got a FF Widgeon (-10F with cont. baffles) that is going on seven years and holding up great. It doesn't get a ton of use since I bought a FF Vireo a couple years ago... that bag with a thin bivysack and a good down jacket works for nearly everything and is pounds lighter than my Widgeon.

I use a Bibler Big Wall Bivy Sac over my sleeping bag to extend the warmth.

It is a little oversized with room for boot liners, extra gloves and sleeping pads and it has a maleable support wire to keep it off my face.

I carry it on long daytrips because it is lighter than most emergency tents and lighter than my sleeping bag.

Western Mountaineering! I'm very hapy with my 20 deg WM bag. Way warmer than the Northface Snowshoe I had that was rated at zero.

I've been using a FF summerlight 30 and adding clothing layers/puffys and bivy to add warmth as needed (carrying anyways). Makes for a lightweight adaptable system. I use a exped synmat and closed cell foam on the snow. Gets me through 3+ seasons. Might be a little rough in the dead of winter at altitude.

Edit... The Summerlight is Westen Mountaineering not Feathered Friends

~2008 synthetic Marmot Pounder Plus "25" degree bag, plus puffy and hat, gets me through four seasons. Don't skimp on the pad. Winter's cold ; I may get a warmer bag (~10F?) in the future for winter use. I'm enamored of the Sea-to-Summit E-vent stuffsacks; they may provide sufficient waterproofness to make down insulation immune to the ravages of rain and creeks.

As an upper bound on warmth, a zero degree down bag and down exped mat is sufficient to stay toasty in any conditions we've experienced.