I noticed that the Apr 24th release has fixed something I found odd with render regions and adaptivity, and now it works as expected, brilliant!
Previously, two odd things happened - first, when rendering a region I got MUCH better results for that region than the same region looked when rendering the whole image, as if the adaptivity was "focused in" on the small region. This made it impossible to use render region to check anything with adaptivity enabled,as the look was different from rendering the whole scene. This is no longer the case, and results seem identical whether region or scene is done.
The other thing was the recalculation passes value - render region would run fast up until it hit the number set there, and then every pass after that was slow. It made render region significantly slower with adaptivity on (for about 15 passes, without adaptivity was 3 seconds, with it on at the default interval of 5, it was 23 seconds). That also no longer happens!
Just wanted to post to say thanks for the improvements there, and whatever changed, wanted to say it did not go unnoticed!
Max 2017, Apr 24th daily