I'm sorry, but I've said it before and I'll say it again right here... The existence of freak occurrences in which all major handgun cartridges have failed to immediately stop an attacker does not mean that all handgun cartridges are equal, it merely goes to illustrate the importance of shot-placement in a self-defense scenario.
Anyone who understands basic physics will tell you that a bigger, heavier projectile has greater momentum and therefore greater force, ergo a bigger, heavier bullet will hit harder, penetrate deeper, smash through bones more easily, and leave behind a larger wound cavity, especially so with Jacketed Hallow Point bullets. All of those factors combined mean that a person who is shot by a bigger, heavier bullet is going to take more damage and likely experience a greater amount of pain, thus increasing the odds of either incapacitation or a psychological stop from non-vital hits to the target.
You'll read a lot of articles online of freak occurrences in which an attacker took several bullets and kept on coming, but few of these articles detail just how long the attacker remained mobile afterwards, and there lies the clincher. Yes, shot-placement is key, and no one should ever rely heavily on uncertainties like eventual incapacitation due to blood loss or a psychological stop, but that doesn't prevent such things from being factors, and personally I would prefer a bigger, heavier bullet like .40 S&W or .45 ACP which in the unfortunate event that I fail to score a vital hit, will likely improve the odds of stopping the attacker sooner via incapacitation or convincing them to retreat.
In closing, if you feel most comfortable/confident carrying a 9mm, then more power to you, nobody is saying that the 9mm is ineffective, in fact I myself regularly carry .380 ACP, but don't go believing or spreading this nonsensical assertion that 9mm is equal to heavier cartridges because it simply isn't true.
Statistics can be very misleading and are often backed by information which hasn't been compiled in equal measure. For example, did you know that based on statistics, .22LR has stopped more attackers than any other cartridge? It's true, look it up. But how can the .22LR possibly have a statistically higher volume of stopping attacks than any other cartridge? Simple, because more people own a .22 caliber firearm than any other cartridge, the .22LR has very little recoil which makes it very easy to stay on target, pull off quick follow-up shots, and these statistics don't take into account how many times each cartridge has failed to stop an attacker, ergo the results are hopelessly skewed and beget misleading results due to an uneven sample size. By the way, this is also true of most statistics, hence why many folks take statistics with a grain of salt.
I bought a 4006 and soon discovered that I couldn't shoot it near as well as a 9mm or a .45acp. I spent two years experimenting with factory loads and just about every bullet and powder out there. Never did warm up to it. 
But at the same time, I'm also a believer in shot placement and ease of carry. Thus I have been known to carry a .38 revolver, .380 or even a .25acp when circumstances called for it. 
