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950g though. What about their race system bags?
http://www.snugpak.com/outdoor/sleeping-bags/adventure-racing-sleeping-system
hippy-
Don't know anything about those.
I've got a traveller:
http://www.snugpak.com/outdoor/travelpak-travellerAnd a chrysalis 4:
http://www.snugpak.com/outdoor/chrysalis-4The traveller is great because it opens up to form a duvet.. so if you're on a pad (which is the most important part of your sleep system in a tent or bivvi) you can double it up on top of you. You can also wrap it around a hammock, or share it with a friend ;) . Its comfy for me down to about 0, when im layered up in a tent. I don't tend to sleep naked in a tent anyway.
In a bivvi i'd be a little worried about condensation, making it harder to keep warm in cold weather. I wouldn't go below 5 or so and stay out of the wind.
The chrysalis is bulky and heavy, but kept me toasty warm way beyond 0c, even in an exposed bivvi. I'm happy camping anywhere in the U.K at wintertime with that, a thermalite and a down jacket.
I'd say don't worry so much about the rating on the bag.. pay more attention to the other kit; your pad and your layers. A hat can be used as a pillow or to keep you warm, a down jacket can wrap around your feet if they are cold, etc.
And 300g +/- is nothing!
Kidneys
Just get the Snugpak. You won't freeze. If you feel the nip you can just layer up. Get a cheap down jacket and some merino. Possum socks! Versatile and cheap.