The problem with high velocity low caliber ammo is that it doesn't transfer energy efficiently to the target. That means it either goes right through you, or cuts you up real bad inside, but it takes a relatively long time to do it, so there is little shock value.
The other extreme is something like a .45 ACP, which is slow, but super heavy, and high caliber. When it hits, almost all of it's energy is transfered at once to the target, meaning massive localized damage. this produces shock symptoms faster and more reliably, and that's why it's a "stopper".
It's like the difference between being stabbed or hit with a baseball bat: Both will kill you, but one will knock you on your ass first.