I'm feeling it at around 40. At 50, 'backers bail on play action too quickly, basically making it totally ineffective. Down to 10, and dogs will actually turn and chace a RB without the ball from behind.
This is something I'm really not done looking at. My big takeaway on that slider through four games is that it has a greater effect on the running game than the passing game, and a much greater effect on play passes than anything else.