Hope to go backpacking/camping this summer, and camp in the winter next year...just wondering about sleeping bags... Most of the ones I have looked at have temperature ratings. If I got one that was good for -30*C weather, would it be too HOT to use in the summer with +30*C weather? Or does it matter? Don't really want to buy 2 sleeping bags, but they aren't THAT expensive. Any brands to stay away from? What are the good ones? What are features to look for? Thanks!