Speed does kill, but it also has to have mass to do so. You take a large cal heavy bullet and push it at the same speed as smaller cal lighter bullet and the heavier bullet will win every time. You just can beat the law of physics. The 5.7 has its place, but I'm just not sold on it being a better defense weapon than the 357 magnum or 45 ACP. Would you rather take a hit from the 5.7 or a round from Ma Deuce

A Doe walks out of the woods today and says, that is the last time I'm going to do that for Two Bucks.