I have no experience shooting humans....but have a had a lot of experience shooting pigs and cattle with hand guns. Shot placment is key...a .22 will kill a large pig with one well placed shot....miss the spot and the pig will act as if nothing happened.
A friend who had no experience shooting animals decided to shoot and butcher his cow. He choose a .25 auto...he placed the muzzel between the eyes (should have been in the middle of the forehead to do the job) at the shot, the cow became very much alive and not in a good mood. My friend grabbed the cow by the horns with one arm and was shooting the cow in the head as they went around and around the door yard...his wife was screeming and the adrenulin was flowing. I ran for the house and retrived my .357 that I was used to shooting and could hit well with it. The cow had drug my friend into the barn and he was holding on for dear life. I told him to let go and get back...which he did. One shot from the .357 between the horn and the eye and that cow dropped like a rock and never moved. The .357 never failed me once ...but shot placement was the key. The .25 auto just did not have the penetration power on the cows skull. I have shot a pig that was popping its teeth at me and would not give me a premium shot, it was going to charge and its snout was up....so I put a bullet right down the snout and followed it up with another through the brain. The pig went down with the round in the snout but was not dead...second round finished it. For me, its about shot placement and having enough penetration to hit the vitals....brain or spine and they are done right now....heart or lungs and you may still have some fight left in them even though they are dying...they can still hurt you. I expect humans will react the same way when hit with a round. Spine or brain and its instant stop....heart or lungs...and it will kill them but it may or may not be instant. just my .02