I agree with Jeff, I would get the Antelope for ranges of 10 degrees to -10. Western also does an overfill (and I believe its 3-4oz more for this model bag). Accordingly, this will lower the temp rating a few degrees (conservatively). I would look into that option if getting this bag for your situation.
I use a Sea to Summit dry sack (20L) with eVent on the bottom. I know the 20L is large for this bag, but with the wider bottom of the bag, and the way its shaped like an oval on the bottom it allows the bag to be stuffed into more of a "cube" shape instead of a long cylinder that never fits well in you pack. And, the larger dry sack allows me to put clothes in there too. either way, it makes a nice fit for my pack.
If you use a waterproof bivy, you could use that as a stuff sack in itself. That way you don't have to use two other stuff sacks (one for the bivy and one for the bag)
Feeling the weight of this bag makes me think that there's no way it could keep me as warm as its rated! I'd been saving my change for a while to get a nice bag and I more than got it. It's so light, and comfortable. I'm 5'7, 145 lbs and i have the reg. I know there's a ton of room in it for me, but when I used it in 23F with only boxers, I was hot. I'm a really cold sleeper, and the only other sleeper colder than me is my brother. I had this thing zipped half open for part of the night just to let the wind blow in my bag.
I've also used it in warmer weather (pushing the down to the bottom/back of the bag), and am stoked to use it in colder weather. Its hard to go wrong with this bag. If you want a bag that really can replace all but your winter bag (for some people it can even do that), this is it.
I once had a hard time converting to down too, especially with that question of survival in a wet bag. But when I reflect on all the years I've used a synthetic bag I've found that any reason my bag got wet was from my own fault. If a person wants to keep their bag dry, they'll more than likely be able to do it.
And as far as synthetic being fine when its wet is a myth. all the times my synth bag ever got wet, I woke up cold and miserable. If a synth bag will make you wet and miserable and a down bag will make you wet and miserable, then I figured I'd go with the one that weighed the less.
This is all from my personal experience, though. Others might have better synth bag experience than me.
The fit of the women's version of the prolite plus is tailored to have narrower room in the shoulder area and more room in the hips, whereas the regular prolite plus (men's version, if you will) is wider in the shoulders then tapers down towards the feet.
It also seems that the pad, like women's sleeping bags, is built with more insulation because, in general, women seem to be cooler sleepers than men. Not always true though, as my wife is a warmer sleeper than I.
This bag has no draft collar. BC's specs are wrong on this matter.
I recently used this bag for a 3 night hike. Temperatures were around 45-50 every night. I also supported my temp readings by checking with www.weather.com before and after my trip for the area I had hiked/slept. However, I was a little chilled when the temps hit about 45 (while i wore smartwool socks, polyester underwear, and polyester tshirt). I was using a big agnes insulated air core and my back/whatever was touching the mat was fine, however, my feet, parts of my legs, and parts of my arms were cold. I am a slightly cool sleeper but have never had a major issue with temp ratings. Normally i'm too warm by morning.
Other things to consider before i went to bed:
-I had a large, warm, spicy dinner.
-Did about 8 hours of hiking and climbing that day
-Was more than well hydrated
-Slept in a tent with other people and a rainfly
I liked the stretch baffling system a lot because it allows you to shift around as if in a normal bed. However, I looked up the specs on the MontBell website to find that there is 10oz of 800 fill goose down total in this bag. The bag does not contain a draft tube for the zipper (a small flap that covers it), and obviously no draft collar (most bags this temp rating don't have one). I looked on Marmot's website to find the specs of the Marmot hydrogen (30), and it uses 11oz of 850 fill down. Although only one oz more, it is higher quality down, resulting (in my opinion) quite a bit more insulation. Marmot also EN tests all their bags. I could not find anything about whether or not MB EN tests their bags or not. I've also looked on the Sierra designs website at the Nitro 30 and its fill with 12oz of 800 fill goose down! Same fill as MB but 2 more oz....thats an eighth of a pound more! My wife has the women's version of the Sierra Designs Nitro (the Spark 30). I climbed in it and there is a HUGE draft tube and zipper guard. the loft is twice the size of the MB ss3 and i was instantly sweating!
I regretfully returned my bag. I believe I will pay more close attention to not just the type of down used but also the fill weight of the bag. If two bags have the same fill, then more down=more insulation=more warmth. Common sense I'll never overlook again.