beside you dont need high OD for a PF... either have enough so that he can play at SF or 7 is quite enough since you are not going to face an outside PF every day... :/
to be honest i though so also a long time,but since i go for OD for both of my big, i got lot more succesful and OD 8 ID 12 bigs could even compete on BBB level(and those two played roughly 40 min for me last season.