[berserk]

Seems like he can easily have 55 or a flush here. I certainly fold here as very few people can make such a big bluff, and when your hand looks pretty strong to be calling the turn he can't expect you to fold the river often. I think if the river is a non-spade 6 it's tougher, as he could be thinly potting something like 78, and as such i think i would call.