For me, that'll depend a lot on how much of a bullet sponge enemies become. I mean, when I head shot someone with a sniper rifle I want them to die. What would really svck is to take that head shot, they take a tiny sliver of damage and then immediately detect you.

I hope theres an animation for a stealth kill. They had some in Skyrim, so I'm going to assume they do in Fo4 as well.