Need to place an order on a M&P15T after Xmas.
Greg is probably the most hands on knowledgable person when it comes to firearms. He's not giving you a biased, news article opinion, he physically fires almost every weapon @ Blackwing. +1 for best service/knowledge in Columbus.
5.56mm will go right in, and right out of someone. With a smaller round traveling over 2,900FPS, you'll have over-penetration. Meaning, it'll go through walls, which is never a good thing. Consider 5.56mm to be mini ice-picks, they go in and go right back out.
Draw up weapon, surefire turned on, assume some sort of corner cover, ID threat, aim weapon center mass, and tap one off. Make sure target is neutralized, dial 911, light up a cigarette, and wait 20 minutes.