Using "over penetration" as an argument for jhp over fmj is a none starter for me. If you ever have to actually pull that trigger to defend yourself, regurdless what type of ammo your using your rolling the dice that it will work out good for you.
A few years ago there was a police shoot out here in Phoenix where the police fired 87 rounds at a BG and only hit him 11 times. I don't care how good a shot you are, when your in a stressful siduation with things are happening quickly there are going to be misses and the type of ammo won't make any difference if you miss your target and hit a bystander.
The way I see it is I want to be sure my round can reach a vital organ and I certainly would not shoot if there was someone behind a BG, regardless of the type of ammo I was using.
If over penetration is a concern you better not ever use a 9mm or a 40cal.
I would also be more worried about misses than over penetration.