FPE is not a reliable way to predict the therminal performance of a cartridge. Frontal are, mass, and momentum or for better in this reguard.
Example the pictures below are exits in the rib cage of a 6X7 Bull Elk (both exits are in the rib cage of the same Elk)
The first picture is the exit of a 180 grain bullet with an impact velocity of 2600 FPS for 2700 FPE
The next picture is the exit from a 440 grain flat point hard cast bullet with a muzzle velocity of 950 FPS and 882 FPE
It is clear from the picutre that FPE did not rank the destructiveness of the 2 different rounds in the proper order.
I have killed Deer with the 45 ACP cartidge, with very satisfing results and many will say that it doesn't have enough FPE, yet the results speak for themselves..