It depends on a lot of factors like what division you play in and what type of defense you play (m2m would require more than 3-2 but of course 3-2 would require more players to have decent OD and of course oh high the JS, HND and PA of opposing wings which even in DIV can apparently be high, like the 50k+ guys I get the 'pleasure' to play against in my own).
But there is no reason to have less than 10 OD at any level in my opinion... I've got 6 players with 10 OD with a sub 125k salary bill.