Ha, ha, I personally prefer not to waist my precious metals any more than necessary. But with the 9 mm the guy was carrying you’d probably need the whole mag to stop the nut.
9 mm is worthless in my opinion ... True it has better accuracy - and perhaps longer range - than a 45 ACP; but it’s stopping power is notoriously weak. As you stated, several shots required to drop a determined attacker. Not so with a 260 grain 45 JHP ... One shot to the shoulder will rip the arm off the perp, and likely result in a “bleed-out” before the police arrive on the scene - which is the way I prefer the situation end.
A 45 JHP shot to the abdomen would tear the aggressor’s insides to shreds, and cause maximum pain - a slow agonizing death. If you are going for the “gut shot,” aim for the liver - a hit there pretty much guarantees a trip to the morgue.
Head shots are tough in high adrenalin situations, unless you are close and really good - as in having practice sufficient to make your reaction completely reflexive.
In all candor though, I am given to understand, by those who are in a position to know the “system,” that - in most states - if you kill the perp with the “triple tap,” you better have a very good lawyer, as it is tough to prove “a lucky shot” with that scenario. Apparently the authorities frown upon the ubiquitous “shoot to kill” attitude - at least when it is not their asses on the line.