Feathered Friends Peregrine - 37.4 oz. down, 3 lbs. 14 oz. total weight. Comfort (?) rating of -25 degrees F.
Western Mountaineering Puma - 36 oz. down, 3 lbs. 7 oz. total weight. Comfort (?) rating of -25 degrees F
The Puma is nearly a half-pound lighter for a bag that is at least as warm. I own bags from FF and WM, and have played quite a lot with many from each that I don't own. FF makes really nice stuff, but overall I find that WM seems a bit better made, bit better fit and finish, a bit more densely packed. That said, when I had a FF Snowbunting and WM Antelope side by side they looked pretty comparable. The Snowbunting in Epic weighs about the same as the Antelope in WS; the MF Antelope is ~6oz lighter.
I have owned and used a number of bags with and without WPB/WR shells. Those shells add some weight; generally I find a normal shell is more than adequate, and feel that the WPB will just impede breathability a bit more. But my experience has been that the WPB shells haven't affected the loft of my bags, particularly in temps ~ -20F to 20F. The best use of WPB, in my mind, is around the hood area and draft collar, to block all your exhalations from saturating those areas. I generally don't have warmer weather bags cinched down that much.