Probably most of the head/neck shots are using either the Magnus Bullhead or the Guilliotine, both are head/neck shot only broadheads. Some people have a hard time getting them to fly good, because of the large 3" and 4" blades.
I agree with IL-cornfed, there are several mech. broadheads with 1.5" - 2" open diameter that are excellent choices for turkeys.