Here's a link to the Brady Campaign video for what the 5.7 can do:
http://www.bradycampaign.org/ler/fnh/
Now I'm going to give a spoiler out...they shoot it with a 12ga slug and it absolutely destroys the vest, but doesn't puncture. It's a belly shot, and they guy who does the video has the gall to say it probably caused massive internal bleeding, but was probably not fatal. I have to say, if it were a chest shot, I'd bet it would be instantly deadly, penetration or not.