Re: PFF's Top 5 and Bottom 5 by Position (Through Week 5)
I think out of all the positions, 3/4 OLB's and all defensive line and offensive linemen are judged pretty accurately.
I've seen them refer to yards per route for WR grades, which is highly debatable to how much that matters. Also, they seem to rate takeaways far less than I would for a defensive back.
One thing I feel pretty confident in for all grades is if you're on the bottom 5 for your position, you've played like sh!t. If you;re in the top five, you're playing very well.