I can't vote, because I think caliber and shot placement are both important. Actually, I really don't think "caliber" is what matters, but rather ballistics. I've always believed that for handguns, a larger caliber is more effective because the velocities required to make a smaller caliber as effective are not attainable with the short barrel.
If you double the size of a moving object, you double the energy.
If you double the speed of a moving object, you quadruple the energy.
The .223 round takes advantage of this by propelling a slightly smaller projectile MUCH faster, so the impact is as hard, if not harder than larger riflecalibers.