I presume you are just talking about what the wrist has to do for those two poses? Since it's all about the the same bone rotating and about two extremes at opposite ends of the motion range, i would say put them in the same smartskin.
Now you have two completely different answers!
Multiple Smartskin keys work best when they are evenly spaced, for example at
-90, 0, 90
or
-80, -40, 0, 40, 80
The fewer keys you can get away with, the better.