First lesson I want you to learn is that only hits count, especially when those hits are aimed at the vitals. Granted you are probably not going to hit as well as you would expect when you are under stress, there are remedies to fighting up close with a firearm. Hip-firing with a pistol up close does not always allow supremely accurate shots, but a hit in the thickest part of the body is still the ultimate goal, or at least aim for the pelvic region.
When it comes to shooting with full extension, I do not believe in any hit being a good hit. This is simply because there are plenty of areas on the body where you can take shots and not even be phased and limited in your ability to respond with lethal force. For this reason, I always practice "front sight accountability" which means that I do my best to ensure that my front sight in on my target with the rear sight roughly aligned to allow for an acceptable impact, as long as I do not move the sights during the trigger jerk, which is inevitable when shooting fast. I have found that a little bright nail polish works well for assisting you in picking up the front sight quickly.
Consider the fact that a gun is not a phaser. It will not knock someone down in one shot unless the person decides to go down. Sometimes a hit to the pelvic bone can shatter that support structure, most likely later resulting in death. But besides that, people have been known to take several chest shots, heart shots, and even head shots without stopping. Unless you eliminate the brain stem, a vital organ hit takes time to lead to a fatality. Now for those thinking that several rounds in the vitals as fast as possible will help, you need to realize that the difference is marginal. You are way better off just hoping they decide to stop. If you shoot them five times in a millisecond, they won't stop much faster than if you shoot them 3 times with three flash sight pictures.
Now I am not telling you that you shouldn't learn to put rounds on a target fast, because that is a key element to defensive shooting. You are supposed to "pump them full of lead" and shoot until the threat is stopped. But what I am saying is that learning to shoot faster is a byproduct of learning to shoot followup shots quickly and accurately under stress. My proposal is simply that you start training to only shoot as fast as you can accurately hit. You will find that this is way more rewarding in the long run. But that is not to say that you shouldn't push yourself occasionally, or else you will never know if you can step up your game. Train hard, train often, and stay safe out there.