Unless you are doing some serious winter camping in extreme conditions a -20 bag is most likly over kill. When buying a good sleeping bag here are a few things to consider. What style, do you want a mummy or a rektangulr, a lot of people can't sleep in a muumy, they find it to confining, but they are the warmenst. What environment will you be in, that's important when looking at differnt insulation options. Down is by far the warmest, the lighest and packs the smallest. I only use down bags, but you need to keep yourself dry. Go look at some sites like Feathered Friends in Seattle, they make a top of the line bag and have lots of good information available to educate yourself. The North Face and Marmot are also good sources. Buy right and you will only have to buy it one time. Spend a few extra bucks, it will be worth it.