Finally had a chance to test the path tracer. The scene is a section of my Erie Canal project and includes models, foliage, and a water surface. (The water is actually a surface layer with a reflective shader plugged in as a child.) Both renders are straight-up conversions from 32 bit, no adjustments.
The challenging thing about this part of the scene is that the foreground is almost entirely in shadow (cast by structures off-camera to the right). The standard renderer seems to have a problem with this. None of the objects in this large shadow cast their own shadows – there's no shadowing inside the rowboat (on the steamer deck), no contact shadows beneath the crate or rowboat and, strangest of all, no interior shadows inside the rear cabin of the steamer or the barn.
The path tracer does a much better job and the shadowing is much more natural. The background foliage looks a bit better, too.
But the water surface has lost most of its reflectivity. Any way to restore that? (I bumped the water's reflectivity from 1 to 2 for the path traced rendering. Originally it was much grayer . . . looked like lead instead of water.)
No GISD on the standard render or surface detail exaggeration in the path traced render. The path tracing took about 8x longer than the standard render. I noticed it really slowed down when it hit the water surface.