Whee, take what works for you.....just be sure it'll function in a survival situation, if you're going to use it in that role, as well as a normal camping tool.
Sleeping bags are a very personal preference. For example, Wiggy's has taken the approach that you're always going to be sleeping outside, with no shelter. As a consequence, those bags are really heavily insulated.
When I attended Arctic Survival Training (Cool School) at Eielson AFB in central Alaska, the instructors emphasized the need for shelter in cold temperatures, as well as cool or wet conditions. With a decent shelter, a mega sleeping bag isn't necessary. In fact, it may be a liability.
I broke an axle on a ski plane, and wound up sleeping out on a night when the temperature dropped to -45. As soon as I realized I was spending the night, i constructed a one man shelter, as taught in Cool School, sort of like this:
http://achievingadventure.com/blogs/cle ... -the-wild/.
I unrolled my "Arctic Weight" sleeping bag inside this very tight shelter, and crawled in for the night. Within a half hour, I was sweating....heavily. Fortunately, the sleeping bag was synthetic, so it still functioned.
I realize that most folks aren't going to be sleeping out in that kind of temperature, But, the point is, if you build a decent shelter, you really don't need a heavy sleeping bag. Even if you can't build a really tight, closed shelter, if you are wearing PROPER clothing, you can crawl into that "less than Arctic" sleeping bag fully clothed, and combine the warmth of the clothes with the sleeping bag's inherent warmth.
Shelter is a very important "tool" in a true survival situation, even in relatively warm weather. A passing shower, really damp morning dew, etc, can defeat many sleeping bags.
And, as someone noted above, an insulated pad is also an essential tool.
For fire starting, I carry a BlastMatch, a Bic Lighter, and a box of lifeboat matches. Plus some fire starter tabs.
FWIW.
MTV