Retained energy really doesn't tell you much, because kinetic energy cannot be directly related to killing effect. For example, a .308 Winchester will produce much greater kinetic energy than a .54-caliber pure lead round ball launched as fast as a muzzleloader can launch it, yet the round ball will also do a creditable job of killing game.

In addition, although I can understand your desire to develop a "formula" that will permit you to calculate the usefulness of a given cartridge or compare cartridges, I do not believe this is really possible, since so many of the factors are more subjective than real. Many have tried in the past, yet the results of such labors is questionable at best. For example, you can calculate the free recoil of a specific load in a gun of given weight, but this number does not indicate how that recoil "feels" to an individual shooter. Some find the recoil of a .30/'06 to be objectionable, but that same person has no problems with the recoil fo a 12-ga. 3.5" magnum goose loadthat in reality delivers three times the free recoil of a .30/'06!

IMO, when one is shooting any of the medium-power cartridges between .243" and .323" (6mm to 8mm) in caliber, using bullets of like construction and similar sectional density, if one places his/her shots correctly, the actual difference in results when shooting the same game is largely academic.

As a matter of fact, arguing which is better, a .308, .30/'06, 7X57mm, 7mm/'08, .270 or .280, etc. etc., is about as sensible as debating how many angels can stand on the head of a pin. A lot of fun, perhaps, but not much else.