I've already put .5u on Sherk. You're right about him only losing to the best of the best: GSP, Hughes, BJ, Edgar. It is amazing that in 38 fights that has only lost to 4 guys, all of whom were--or later became--UFC champions.
With that said, taking the lead from PP and getting MMAthematical up in here, his performance against Griffin was not nearly as dominant as Dunham's. It was actually a very close fight, while Dunham basically handled Griffin 80% of the way. I think that Sherk will primarily have problems with Dunham's height and length. I think that Dunham will be able to keep him at bay and if they do tie up, I actually think Dunham's going to get the better of the grappling exchanges, just as he did with Griffin and Escudero, both of whom are known as good wrestlers in their own right.
So yeah, .5u on Sherk. Hopefully he can pull it off. But if I can get Dunham at a better price, then I would take him.