9x19 or 38+p and up is plenty with good shot placement. You might need a double tap compared to a single shot from one of the really gnarly loads like 357 mag or 45 acp, but there are so many variables in these situations, who knows how they shake out? The person who gets the best aimed shot off first with a decent caliber is the one likely to walk away - if they have luck on their side that day. The arrangement of the human body is complex and variable, so any load can fail if it happens to miss something vital. If you hit someone in the heart, kidney, liver, spleen, or a significant vessel, they're gonna be down pretty quick from blood loss shock, almost irrespective of caliber. Again, though, bigger hole = more bleeding. Medical tip here for you guys - in most folks the left ventricle of the heart sticks out just to their left or to your right next to the sternum (breast bone) about 2-4" above the midline of the torso. Big time blood loss there. The sternum is not too thin actually - pretty thick and tough. In my mind a lower chest shot slightly to their left or your right of center is better than dead center or high. Hitting anywhere in the chest and collapsing a lung wouldn't be too pleasant either. Another great place is the upper abdomen - their right side your left - big huge liver right there that bleeds VERY easily and no sternum in the way. Honestly, it would be hard not to hit the liver if you aim upper right abdomen. I'm not a big fan of head shots - too risky I think. Too easy to miss. Basic fact is that with a larger and heavier bullet traveling at a faster velocity you are more likely to get below superficial and hit something important. I would think a 9x19 147 gr out of a significant barrel length - say 4" - would accomplish that goal fine with good shot placement. Of course, some people use a lighter bullet. I just wouldn't get too light.