RE: Head shots?
Personally, I never had, however, I did recommend that my friend take a head shot.
We were trailing his liver/stomach hit buck after waiting6 hours. We tracked him about 200 yards. We were on our hands and knees trailing just specks of blood. We came upon the buck which was bedded (we were not sure if he could get up or not). He was only about 5-7 yards and his butt was directly facing us, his head turned sideway (he had his head up).
My friend had a passthrough through the skull which put him down right away.