I've always practiced the "Mozambique Drill" where you practice shooting two qucik rounds center of mass then an aimed shot to the head (ocular cavity). Even if the bad guy is wearing armor the two to the chest will slow him down enough and/or stun him to allow you to place that aimed head shot.
I think buying a 5.7 or looking for penetrator rounds also means a round could drastically over penetrate if the bad guy weren't wearing armor. Then you're talking about rounds going through walls and into the streets or neighbor's house.
And the money you save on body armor or a 5.7 can be spent on range time to work on the drill.