Speaking as a physicist, but not a ballistic wound expert...
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Overall penetration is over rated in my opinion since you want the bullet to deposit its energy into the target, rather than passing through it.
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Depositing energy into the target is good; however it is possible for a bullet to deposit energy into a target without doing real damage. A bullet does most of it's damage via penetration; if it hits a bone and stops (without doing significant damage to the bone), that energy has been dissipated in a relatively harmless manner. Consider a bullet stopped by body armor; it'll leave a nasty bruise and maybe break a bone, but it's a
much more survivable injury due to lack of penetration. A bullet which expands to huge size but only penetrates very little into the body might be stopped by skin and muscle, causing a horrible wound but not a life-threatening injury even though it may have as much energy as a .45 ACP round.
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The results are interesting, but also not conclusive. They don't show the ballistic gel so you can't see how big the temporary and permenant crush cavities are.
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I disagree. You can estimate the wound channel size from the penetration and expansion data. But I'm of the opinion that the overall volume of the wound channel is not as important as having sufficient penetration (not too much, and definitely not too little!) and good shot placement. The idea is to stop someone by hitting something vital, not make them bleed out after they've bludgeoned you to death with your own gun.
The ideal defense round will expand as much as possible yet have enough energy to completely penetrate the target, with essentially no energy to spare after that. I've seen other posts describing bullets being found in clothing after traveling all the way through the target's body; that is the ideal, perfect terminal ballistic. Further over-penetration wastes some energy, but that's only a problem because it could be a risk to something or someone behind the target.
As for expansion diameter: the somewhat higher expanded diameters in .45 do not directly translate to substantially greater "stopping power," which requires hitting a vital organ, usually the central nervous system. The size of the bullet matters little; an extra 0.1" in diameter doesn't make much difference unless your shot missed nicking something critical by 0.05". Clearly, that is a small distance so it really doesn't matter. The bullet just needs to be large/heavy enough so it can have sufficient penetration to reach and damage something vital.
Based on this Winchester data, it looks like a toss-up between .357 Sig and 9mm +P. Indeed, the .40/.45 also have similar performance to .357/9mm, with perhaps a slight edge to the .45 (but it's not a huge difference, and it's only because the .45 round fully expanded even after passing through cloth while the 9mm and .40 did not).
I've seen several "caliber war" discussions where people say things like "only choose a caliber that starts with .4" or "the .45 has superior stopping power" etc. But really, look at the data: there are no huge differences in performance. They all have similar, adequate penetration - by design, I'm sure - and they all expand reasonably well (some less well when going through cloth, which is why I like what I've heard about Corbon DPX... though I don't have any, due to cost). I imagine smaller rounds would be less effective, though I haven't seen much data.
If you don't have to worry about over-penetration and hitting something behind your target, I think ball ammo is great - especially for military purposes, where you might need to shoot through cover or armor. The wound channel is smaller, with perhaps about half the cross-sectional area, but it's still plenty big enough provided you hit something important.