Well, you did not use exit portals, and in the other hand, PT, EP and direct sun light do not cope well together.Mor4us wrote:maybe one of the devs could at least take a statement to the heavy grain? maybe i did setup sth wrong?
Since the scene seems not to fit in your GPU RAM(?) in order to "brute-force" (but smartly ) the render, bidir + MLT is strongly advised. And, therefore, Exit Portals (they love bidir).
Did you seek optimizations for the displacement ? I'd recommend that pixel size and planarity (angle) optimizations would be used.
Bidir + MLT is the key, because it's an even better technology than GPU can use. Whatever the reason though, that combo is a must in case of doubt.