What about a neck shot? I got my 6 a couple weeks ago in the mid-neck and he didn' t make it 5 yards after the hit. I have made neck shots with my bow in the past with very good results and have never lost one to it. My thoughts are that if, for some reason (profile shot)...
I hit high = spine shot
I hit middle = jugular
I hit low = windpipe

He' s done either way with little margin for error. I try for the double lung when available, however.