One thing to keep in mind is that Rsk is VERY unstable when trying to measure it on real surfaces. A single pit or pore can drastically change the result. A better approach might be to look at average valley depth (Rv ISO, Rvm ASME) as compared to average peak height (Rp ISO, Rpm ASME)...
The standard deviation of peak heights could certainly be calculated from 3D data sets. However, the challenging part is in the determination of "what defines a peak".
Is it any local maxima, regardless of its position? Then you would have to count a small bump in the bottom of a pit.
Is...