I am considering purchase of a new down sleeping bag to lighten my pack and facilitate use of a smaller pack as well. However, it is difficult to compare different sleeping bags without knowing how much they can be compressed within a compression sack. I believe most manufacturers list a "pack size" but this is the size of the stuff sack they provide and not a sack with compression straps.
How far can I compress a down sleeping bag? I am looking specifically at the Feathered Friends Swallow 20 degree regular bag. This bag comes with a 9L sack but if anyone knows how small this bag can be compressed I would greatly appreciate it.