I've spoken to Marines that got shot while overseas, they say that getting hit in their plates is like getting hit in the chest with a sledgehammer. Thankfully I never experienced that while deployed. I have, however, had the opportunity to shoot at some plates myself and I can verify that those things seem to stop ANYTHING.
First few shots was with a rifled 12 gauge slug; the ceramic shatters but the kevlar fibers kept stopping the rounds. I unloaded 4 magazines of 9mm with 8 rounds in each magazine after that and I never was able to get a round to go all the way through. A 9mm round on an unshot plate was like shooting a BB gun at a brick wall.
I didn't have the plates in a carrier when I was shooting them so I imagine the stopping power is further increased when they are in the carrier since they would be held together better. Unfortunately, none of us had any 7.62, that was the test we were really interested in since all of the guys we were fighting overseas had AKs.
