Josmund, if 900 FPE was required for an ethical kill than I don't know how our ancestors survived using just a plain old round ball. If you run the numbers through a ballistic chart for a .50 cal ball at 1400 fps here is what you get:
Input VariablesFirearm typeRifleSight Height1.0Bullet Weight (grains)230Ballistic Coefficient.075Muzzle Velocity (fps)

Ballistics Table in Yards190 gr., .073 B.C.www.hornady.comRange Energy (ft.-lb.)Muzzle:827, 50 yds: 516

So the 900 FPE is a number that someone shot out many years ago and for some reason it stuck. Three are many things that need to be considered besides energy. Some include frontal mass of the bullet which determines how the energy is going to be delivered to the target AND penetration(how far will the bullet enter the vitals).
If I were to be charged by an angry bear and only had one shot to save my sorry butt I would much prefer the lowly .50 round ball with its 1001 FPE over .223 with is ME of 1232 FPE.

It is sometimes best to live by the old adage: Believe none of what you read and half of what you see.