Several good points in the posts above, and a little bit of confusion. Let me add my 2 cents.
Shooting pins off a table does not translate well to handgun use on people. Momentum knocks those pins off a table. Handguns do not carry enough momentum to "knock" a person down. Physics prevent this: if a bullet will "knock" a person down, then the recoil would also knock the shooter down as well. People fall down, collapse, etc, but are not "knocked" down by pistol bullets.
I've seen a few thousand handgun gunshot wounds, over 150 resulting in death, and attended many autopsies as a result. With modern expanding hollowpoints, (HST, Gold Dots, etc) I could not tell a difference in a person's reaction after being shot, or the resulting tissue damage from the projectile, based on caliber. If there is any difference I missed, it is miniscule. Non expanding bullets are different, bigger caliber usually means a bigger hole (increased wounding) but even then, the person shot doesn't react much different.
What does matter with handguns, is shot placement. Ive seen a 300 pound man take a .22 lr 40 grain roundnose to the armpit and collapse and die within seconds, and a little skinny kid take multiple .45's to the torso, never went down and recovered after a hospital stay.
My advice is use a good bullet (I prefer HST'S but there are several similar designs) of sufficient power (.38 special on up) that you can shoot accurately under stressful conditions. Shot placement is the most important factor, then bullet design, only then does caliber enter into the equation. The handgun projectile should expand yet penetrate through the vitals. Ive seen where a 185 grain Winchester Silvertip centerpunch a person a bit low, frontal through the stomach and came to rest against the person's spine, fully expanded but did not break the spine. The fight continued. A bit more penetration wojld have taken out the person's spine and ended the fight.
As an aside, I prefer a high capacity 9, as repeat shots are faster due to less recoil. In the woods, I carry a 10mm or 454 where additional penetration and power may be needed for animals much larger and with heavier bones than humans.
