Great images and nice details.
Fellazb : I also use PT+HD on exteriors, and I found that I got the same result in half that time. Especially regarding noise.
This is probably obvious but, if PT samples are increased for 16 - 32, then the pass time doubles.
If 16 PT samples takes 15min per pass on a 2k image, then 32PT samples would be 30min etc.
( btw this is on my AMD, will test once I get my workstation ).