I have the Arc Specialist with an Epic shell and 2 oz overfill. It weighs right at 18 oz. Keeps me warm down to at least freezing with just a baselayer. Packs down to nothing and good quality 800 fill down that perks right back up. Even at freezing I have not had to tighten the straps on the bottom. Once you go quilt you don't go back. The freedom of movement is unbeatable.
I also have an Arc Alpinist with 4 oz overfill that is my winter bag. I have slept down to single digits in the Rockies and been perfectly comfy, using an Exped Downmat 7, cannot recommend that highly enough either. The only caveat as a winter bag is something on your noggin. Nunatak makes a down balaclava, I wear my R1 Hoody and the BMW Cocoon Polarguard Balaclava from the BackpackingLight.com website. My quilt weighs 1 lb 14 oz and will keep me warm to at least zero, and with a down jacket even lower.