Tom I have a WM super Kodiak but it was way too large for me and I modified it with two internal elastic straps that hold it close to me. Fit is as important as any rating and I mean I've seen guys freeze in a -40 bag when I was toasty in my -5 bag with my jacket over me. You have to try on a bag and it must have a well engineer foot box so that your feet do not poke through the insulation, especially if you sleep barefooted like I do. The body must fit you just snuggly enough to stop internal drafts without making yu claustrophobic, The hood must be good and it must close down to a small hole, and it must have those shoulder pad thingies to insulate your head area from your neck and chest. A single draft tube is not a good idea unless its overstuffed - mine is.
Jim