Thank you for publishing this report! Your review confirms my choice several years ago of Western Mountaineering (I have the Ultralite).
I'm a cold-blooded female who absolutely insists on a 20*F bag! We've had a couple of threads here recently from other women who also have trouble keeping warm. We cold folks (most of us female) need the equivalent of your insulating jacket and pants plus at least a 20* bag! I camp a lot in shoulder season and take at least one long summer trip to the high Rockies (to date, the Wind Rivers), where nighttime temps are usually below freezing and often get down in the mid-teens. I tried a 30*F bag (Marmot Hydrogen) 6 years ago and was shivering in the low 30s F even with all my insulating clothing on. Not all of us are created the same!
The reason I like a full-length zipper is that I have only one bag which I use in a variety of conditions. On many of my summer trips the evening starts out warm but it gets quite chilly by morning. On warm nights I often start out with the bag completely unzipped, zip it part way up about midnight and all the way up about 3 am. It's basically a question of weight vs. versatility. I prefer the versatility; others (like Will) prefer less weight. I suspect that if you ask other full-length zipper fans that they also want it for ventilation for warm nights. YMMV, HYOH and all that!
I suspect that if more of us demanded it, more companies would use the EN2
13757 ratings. They need, though, to be encouraged to publish all the ratings, not just the one that hopefully keeps you from dying of hypothermia! Unfortunately, once we get a sleeping bag we like, most of us usually aren't shopping for another.
I'm looking forward to the state of the market reports on down pants and jackets!