My observations on hunting and my incoherent rambling.
Velocity= trajectory. KE= penetration. When I look at ballistic charts and I see a velocity figure versus another I think faster bullet, flatter trajectory. When I see KE on chart, I think more KE, more penetration.
Observations on hunting:
Unless it is a CNS hit, the animal dies from blood pressure loss, which takes time. The average time it takes for a deer or similar animal's blood pressure to drop to the point they "pile up" is around 8-12 seconds. I have read this in a number of hunting mags and tested this theory myself over the years. I take hunting and gun rags with a grain of salt, but this has been proven to be fairly accurate too.
When a deer runs for 100 yards after the shot it it usually takes about 10 seconds to cover that distance. I'll take a conservative estimate of speed at 20mph (300' at 10 seconds= 30fps) based on the above figures. This runs is like an average deer, from a mature buck to a young doe or fawn. Average "tail up" speed is usually 20-25mph.
I use this to estimate distance ran after the shot if I can't eyeball the animal the whole time. I figure about 10 yards per second on a good sprint, being conservative, makes a good starting point. If I hear the animal running through the woods for 5 seconds, I figure it will be about 50 yards away from where it was hit. Over the years, this has held to be pretty accurate. I think the top speed for deer is probably closer to 25-30mph, but this gives a good estimate for field use.
Basically, the thing working against us is time.
I think the kinetic energy figure gives an estimate of the penetration of that particular projectile at that velocity. Velocity and energy are interdependant on each other. The higher the velocity the higher the energy. A KE figure gives me an idea of how deep it will penetrate into a body to reach the vitals. That is to say the same bullet with different KE figures, the one with more KE will penetrate deeper. KE is dependant of mass and velocity. Bullet design is also a factor and not taken into consideration for purposes of my ncoherent ramblings.
If a bullet reaches the vitals, it has done its job. That is what I want it to do. If I shoot a solid, non-expanding bullet at an animal, and it reaches the vitals, the bullet did the job. It entered the vital cavity and did damage, leading to blood loss and subsequent death of an animal via catastrophic blood pressure loss.
Expansion is just a bonus for me. I use larger calibers in handguns as a sort of "insurance policy" of an expanding bullet failing to expand. If a .45 caliber bullet fails to expand, at least I have a .45 caliber cutting diameter in the target doing damage (causing blood loss). Expansion is like a coefficient of damage. A .45 caliber slug that expands to .9 caliber does twice the damage, since the damage is basically the leading edge of the bullet doing the cutting of living tissue and not the shaft of the bullet. I don't get hung up on temporary vs. permanent wound cavity. A bullet twice the diameter of another will (theoretically) cut twice as much tissue resulting in twice as much damage and more, but not necessarily twice as much, blood loss, resulting in the incapacitation of that animal.