Ahh, great to see the comparison. The new clouds are definitely better! To my eye PT doesn't make as big a difference here as some scenes, but with the newer shadow placement I bet the non-PT version would look noticeably less realistic in those shadowed areas of the mountains that have trees.
As far as performance, 8x longer seems a bit much to me. It's probably time we update our render setting recommendations and include some info about PT and the new Robust Sampling option for anti-aliasing. This ought to be a big help for PT render performance. So if it wasn't in use in this case, I'd recommend you try it (it's in the Edit Sampling options for AA). It works best with higher levels of adaptivity, at least 1/64th first samples for instance, but up to 1/1024.
- Oshyan