Bought the Go Pro Hero 4 the other day and did some testing with it. I used the suction cup attachment and mounted in at the top of the back window in the center, using the vertical defrosting line as point of reference.
Only settings changed were:
1080p 60fps - narrow view
Up/Dn - Dn (camera is hanging upside down)
Overall, love the narrow view, tell me what you think.