Related to W in nuclei, I had some intriguing plots. here in this thread:
About Z, look again at the two dimensional histogram (actually, a contour plot) of
the attachment. The Z line is painted paralell to the W line, a bit hidden because it seems less relevant. Still, the nuclei with a mass slighy greater than the mass of Z seem to be more stable than usual, or at least no so many beta rays are known, for them.