Will and BPL,
I'm very surprised to find that you omitted what is arguably the best and lightest sleeping bag of the bunch - Enlightened Equipment's Enigma Pro. I own the Enigma, Zpacks and Montbell bags and can without a doubt say the EE and Zpacks are easily at the top of the list for warmth comfort and weight. EE bags inches to the top, however - fantastic design a super compressible. I would like to see more attention being paid to cottage makers on this site as they have by far the best gear for what a lot of people on BPL are looking for.
I think many others will agree with me on the above. There is no hood, but that's where a light down/synthetic hat can serve a double purpose for hiking, camp and sleeping.