In reply to dutybooty: -30 is horribly cold; not sure I'd want to be bivvying on a route at that! But I tested the new ME Snowline last winter and it's good to -23, i.e. you can sleep fine in it without ridiculous amounts of clothes on
http://www.ukclimbing.com/gear/review.php?id=5328 I'd seriously consider the next warmest one up, the iceline I think.
The North Face one might be great and its a good price but I'd want to know what sort of rating they're using for -29.