A couple of reasons to stay away from the over:
Oliver Perez. Though his stats have been horrible thus far when he is on he is outstanding. He took a start or 2 off to work out a stiff shoulder and poor mechanics.
Pirates offense. Though they have been doing better of late they are still last in all of MLB in runs scored. I don't like Jennings but he just might be able to stay out of trouble against this offense.
I have no feeling either way on the over/under but there are a couple of reasons to stay away from the over.