Toroidal inductors - Heat Problem
The core is clearly no good .It would be fine for DC but not for big flux swings .Your 2 switch foward convertor has good efficiency with a good coil.You could do better with maybe a Cool Mu type or better still a EE type if your budget will allow it .If you must make the crappy coil work you will have to reduce the flux swing which will come with penalties .The really bad thing about powdered iron is that it ages with temp and time .The core actually gets more lossey and gets hotter and gets even more lossey .This can and does lead to thermal runaway .Even if you do your temp tests and things are acceptable they may not be in say a years time .If you ran your hot coil for a few months you will find that it will be hotter and the efficiency will be less than 87% .In fact 48V PSUs are being recalled by a credible manufacturer due to output choke burnout while I am writing this .