As mavracer mentioned, bullet momentum will often be more important than kinetic energy of the bullet, especially for penetration. Mass is the more important component for momentum and velocity is the more important component for kinetic energy. You can see this in the formulas where M is mass and V is velocity:
Kinetic Energy = 1/2M x V2
Momentum = M x V
Jim's Rules of Carry: 1. Any gun is better than no gun. 2. A gun that is reliable is better than a gun that is not. 3. A hole in the right place is better than a hole in the wrong place. 4. A bigger hole is a better hole.
no guns = might makes right