The factual and historical inaccuracies in this post are pretty bad. The 9mm was never designed to wound, it is a killing round, just like the .45. And the .45acp never showed up in the Phillipines, and there is virtually no commonality between the .38 Long Colt of that war and the 9mm Para developed in 1908.
Not only that, but the .45 caliber guns that DID make it to that conflict (soldiers were sent leftover SAAs in 45 Colt while the new pistol project got under way) didn't make a damned bit of difference in terms of successfully stopping the charges--a part of the story nobody ever remembers. And at that's with a bullet that was moving at the same velocity as the first ACP rounds and was 30 grains heavier.
Men who are under the influence of chemicals that reduce pain and increase aggression are not stopped by trauma, they're stopped by shutting down the nervous system, and that means brain and spine shots, though heart will usually do it too, or catastrophic damage to key points in the skeletal structure that mechanically impede movement--has nothing to do with pain, it's just that the joint (knee, hip) actually no longer works. When that happens, it doesn't matter if it's a 38 in the brain or a 45, motor control shuts down and the person stops. If it doesn't happen, the person can survive long enough to finish his charge, even if he'll die afterwards.
My point is not that a 45 hits no harder than a 38---it does. However, "harder" is a relative term. The movie images of people being shot with any pistol--yes even the beloved Dirty Harry movies--and flying backwards are fantasy. Take a ten pound steel plate, hang it at a deflecting angle to you (and to anyone else) so that it doesn't ricochet in your face and shoot it with the handgun of your choice, short of the .475 Limbaugh or 500 magnum. You'll notice that the plate bounces a little bit, and then settles down again. There is no way that this translates into a 200 pound man becoming airborne after being hit with the same bullet. Hell, a 30-06 hits with nearly six times the energy of the best 45 ACP available (and creates a MUCH larger wound channel) and I've never seen a deer go flying. Actually, I've seen a couple absorb the shot and take off running for three miles, the bastards!
Point being, handguns of any caliber, shot poorly, have very little stopping power in terms of disabling a truly determined, fearless opponent. Fortunately, in spite of what gun magazines would have you believe, fearless opponents are few and far between--especially in urban environments--and most who are shot AT (let alone hit) will lose bowel control and retreat. Even those "hopped up" are not necessarily hopped up on anything that's going to improve their fearlessness or focus--in fact, most popular drugs on the streets have effects that run the other way.
As to the idea of a small or "one hole" group being useless, never fear---your fine motor control is going to take a serious hit under the stress of a defensive situation, and also unlike the paper your target will be moving. Even if he freezes, after the first shot, he'll move. Being able to acquire your target quickly and hit consistently in the kill zone while you're moving and in less-than-ideal light conditions is very, very much worth practicing, but don't give up on the fundamentals of trigger control, sight picture, etc. I deal with a bunch of cops (usually the younger ones) who are rapped up in fast double taps and rapid fire strings who never learned the fundamentals, and it's pulling teeth to make them slow down and do it correctly. Those who listen get better. Those who don't continue to suck. Shot placement is stopping power.
The best piece of advice here, and it's been oft-repeated, is to be comfortable with your weapon. If it fits you, if you like shooting it, then you'll make the time to practice and will improve. If it doesn't and you don't, then you won't. Worry not, either, about claims regarding "dinosaur hammers" and other such nonsense. Most of those (not all, but most) come from people who've only ever achieved competence with one specific weapon and want to think the others inferior so that they feel better about it.
From what experience I've had with it (only 9mm) the HK P30 is an extremely fun and comfortable gun to shoot. You're likely going to have a bear of a time concealing it, though---HK likes big, blocky slides and this is no exception. Of course, the same is true of Glock. If you like it, and do want to conceal it and try carrying it, then don't skimp on your holster. Take a look at Milt Sparks, Nossar, Bullman and TT Gunleather. Yes, there'll likely be a bit of a wait--you can cheap out in the meantime with a basic one from somebody but don't forget to order the real one. A holster that properly conceals a gun protects you from it (sights, hammers and the edges of slides can wear holes in your clothes really quick), distributes its weight properly on your belt, and keeps its shape despite being next to a warm, wet human all day. I've carried a full size 1911 every day for years, and though I'll admit switching to a scandium frame a few years back, the deciding factor that keeps it on my hip is that I often forget I'm wearing it---the sign of a good holster.