As to power, its all over rated. The right bullet in the right place is all it takes. I have more than a few deer with 223 out towards 600 and never an issue with that.
I have not had a problem killing deer(s) and pigs with a 5.56 either, OTOH where I have hunted all my life in the southeast a good blood trail is pretty important, blood trails with deer I have shot with larger rifles have always been a bit better when well hit than what a 5.56 has given, this may have been bullet dependent as I am most familiar with the tsx bullets in the 5.56. Yes I am sure the AR10's I had would deliver better than 2 MOA with extensive reloading efforts and with an expert shooting them.
