"Stopping power" is a misnomer. The larger and more powerful the round, the bigger the hole, resulting in more damage. You can't stop the forward progress of an attacker with a handgun round. Even dead, momentum will keep the corpse coming.
Even heart shots might need to bleed out for a brief time, and history is full of people who have had large portions of their brains destroyed and gone on to live relatively normal lives. Take Nancy Pelosi for example.
I firmly believe that the "X" on any silhouette target should be somewhere between the tip of the nose and the Adam's Apple. No skull to speak of, very difficult to armor, and it's a bee-line to the medulla oblongata. Even if Elvis doesn't leave the building, the threat is guaranteed to be over when you hit the interrupt switch.
One thing I've never understood about the Mozambique technique is why the kill shot is last, or why the time spent on body shots isn't dedicated to severing the spine below the skull.