get the hooded bag - i spent about 7 hours shivering - hard and terrible shivering - in 40F weather trying to use a wool blanket and winter running clothes.
after that i got a nice REI bag, hooded. now when i'm cold i zip up and close up - only my nose is out in the cold.
it can get really cold in July on Lake Superior: https://lh5.googleusercontent.com/-c...o/DSC02299.JPG