'Over penetration' is one of those mythic topics gun writers love when they are promoting the latest wonder bullet design. Ranks right up there with the mythic 'cop killer' bullets of the Clinton era. Even sub-sonic .22 ammo can 'over penetrate' under the right conditions.
I live rurally with a wife and dog. My closest neighbour would be very good rifle shot. A .50 Barrett would be about the only firearm that would be a concern re: over penetration. I hear shots on a regular basis; sometimes it's guys plinking or taking a shot at a coyote or bear. I've yet to hear of any collateral damage.
If you live in an urban or suburban environment, the equation changes. Regardless of calibre or ammo type, the variables are endless - calibre, ammo type, wall material, etc., etc., etc.
Win lose or draw, you can bet your last dollar (and you probably will) that a lawyer will be adamant that firing ANYTHING constituted a risk to public safety and you were acting as a wanna-be 'Rambo' to prove your prowess with a gun.
To fire or not to fire in a potentially life threatening situation is one of those split second decisions that will have a dramatic effect on the rest of your life. People trained in self defence that use deadly force are subjected to stringent debriefing and offered post traumatic stress counselling.
The average citizen is on his own. He may have survived the incident, but is now fighting for his life in both the court system and the court of public opinion, the media painting the blackest picture possible of the shooter.
Jeff Cooper said that the court battle was 'Battle #2' and can be fought, but it matters not if you haven't survived 'Battle #1'.