It depends very heavily on the penetration you're getting. 1:4 would probably be the bare minimum to beat the game - as in pennies per hour - and 1:8 would probably be the bare minimum to beat the game for any appreciable amount of money. 1:12 would probably be more reasonable if you're not getting spectacular penetration.
also depends a great deal on if you are playing all or wonging. 1-4 playing all is probably an even game at best. 1-4 wonging in on plus counts is still a winner.