Hm...didn´t get troubles with render region so far. Though it seems, that the Vray buffer renders faster. Perhaps get in contact with the support guys at chaosgroup if you have trouble.
Well, the color setting I choose deliver the best results for indoor/outdoor ligthing. These are used by many tuts and tips around Vray on the web. Of course you could do all this in post, but this way you can get your render already near the look that you are after. All the color curve stuff back and forth is quite heavy to understand, in my eyes...Playing around with these setting will gave me some idea, though
...sorry, I don´t know. Post you questen at the Vray forum at chaosgroup. They might can tell you. By the way, please use URL tag