Having assisted in quite a few autopsies of shooting victims, I can attest to a few things;
Pistol rounds are way under powered to be a reliable stopper, unless the rounds go in the snot locker.
The minimum standard response for pistols should be 3-5 rounds before assessing.
I've seen 380 rounds get stopped cold in the pelvic area, specifically the ilium and pubic bones.
I've also seen the bullets sail right on thru without hitting anything but meat. From the diagram posted on the first page, you can see the areas where that might happen.
On the other hand, like has been said, the pelvic region is a on-off again target...ugh. If its the first shot you have, take it. You pump enough rounds into it, it'll drop them, but not put them out of the fight unless they decide.
Remember, a person can live 2+ minutes with a clean heart shot, and a lot of damage can be inflicted in that amount of time. So the more rounds pumped in creates more holes, which means loss of blood, lower the blood pressure and the end result...they faint. If you can't get a head shot, make them faint really really fast.
I agree with Clint, get what you can. I can't recall a gunfight where someone did the failure drill...2 to the body, one to the head. or the old...a few rounds to the body, then to the pelvic area, then end up into the head. Its hit what you have available as many times as you can. Most don't have the time to detail pick where their shots go. In the end, I would not discount the pelvic area, its just not the first choice.
Great thread topic...I think its a forgotten target.