In handgun cartridges for SD, kinetic energy doesn't matter much and one should not place such a high priority on it. Shot placement and plenty of practice with a reliable weapon is the key. Next is choice of bullet and its construction. Then choice of caliber (within reason) is the last priority.
I don't place energy as high on the priority list as you might think. My previous comments were assuming that caliber and gun have already been chosen and that speed and marksmanship are separate issues, I'm looking solely at ammunition selection.
As far as energy not making much difference, well sometimes it does and sometimes it doesn't. The problem with ballistic gelatin is that it only tells you half the story: it predicts how the bullet will react to striking the target. What ballistic gel doesn't predict is how the target will react to the bullet. The way that kinetic energy causes damage to a living target is by temporary cavitation stretching tissue beyond its elastic limit. As has often been pointed out, many tissues in the body cannot be stretched beyond their elastic limit by the temporary cavitation created by common handgun energy levels. However, what is often overlooked is that the human body is not homogenous and different tissues have differing degrees of elasticity.
Skelital muscle, for example, is quite elastic and would probably suffer minimal, if any, permanent damage from handgun-level temporary cavity. Liver tissue, on the other hand, is not very elastic at all and would suffer a great deal of damage from handgun-level temporary cavity.
Similarly, air-filled organs such as the lungs are much less sensitive to temporary cavity than fluid-filled organs such as the heart. A shot through the lungs would probably produce relativley little damage beyond that of the permanent crush cavity. A shot through a blood-filled heart ventricle, on the other hand, would be much more devastating not only because of the permanent crush cavity, but also because the temporary cavity is likely to cause profound damage to the rather delicate atrio-ventricular valves.
Back to the comparison between the 127grn +P+ Winchester Ranger and the 147grn version, both loadings display adequate penetration and reliable expansion. The difference between them is not enough, in my mind, to offset the disparity in energy between the two loadings.
Also, I think the FBI's standards are often misunderstood. The 12" minimum penetration standard is, for many situations, more than is needed. As was noted before, the upper torso of an average adult man is 9-10" from front to back, so a straight-on shot with a loading that meets the FBI's criteria would, in all likelihood, be a through-and-through shot. The reason that the standards are seemingly overly deep is to compensate, as has also been pointed out, for a shot that must pass through an extremity or other intermediate barrier or a shot at an oblique angle. Even if our bullet must penetrate 3" of forearm and then only penetrates 9" of torso, that's still sufficiently deep to reach the vital organs.
If you really think you need more penetration than what a medium weight bullet for a given caliber can give you, I think you'd probably be better served by switching to a larger caliber than by switching to the heaviest loading avaialble.
