I brewed up a Peanut Butter Chocolate Oatmeal Stout two weekends back. Used Marris Otter as the base and also had a 8% Victory as those two give off a nice nutty flavor to me. I used 130z of PB2 at the end of the boil. Tasted the hydrometer sample last weekend and it had a nice peanut butter taste to me. Its still early in the process so hard to say how it will end up but I don't think I will add any more PB2 in the secondary.
Another thing I have heard from PB2 users is that the peanut butter flavor picks up a bit over the first couple of months after carbonation so keep that in mind too.