With mortgage REITs (REM -1.7%) tumbling again, KBW looks at where a floor might be found. As a whole, the group is trading at an "unusually large" discount to book value in the teen percentages, but there's no reason to believe it can't go to 20%. While "gravity tends to pull it back toward zero," history has proven these discounts can pervade for a long time. Not surprisingly, those mREITs that have managed through a full cycle before sport the lowest yields and discounts: Capstead (CMO -1.2%), Hatteras (HTS -0.5%), Anworth (ANH -1.1%), Dynex (DX -1.4%). Annaly (NLY -1%) may not make this list because of the passing of Mike Farrell.