I'm debating whether or not to buy my wife a new sleeping bag for our upcoming winter trip. She is currently using an REI Sub Kilo (rated 15 degrees) year-round, but last winter she was cold. (We were at 7800' with a low of around 20 F with winds up to 70 mph, so probably much lower with windchill). Do you think the Marmot Helium would be significantly warmer than the REI bag? I'm afraid that REI's ratings aren't really accurate.
Or…should I just get her a 0 degree bag? I don't expect us to encounter any temps below 15-20 degrees. Lower than that, she likely won't go.

