Well i'm not an expert in this topic. But i think the xt660z for touring may be better for the fuel capacity 22liters vs xt660x 15 liters, this means less stops to refuel.
In the other hand the xt660x for city and commuting may be better and maybe more confortable, i don't know
The rest is personal preference, like, if you plan to use it more in off road than pavement i also would consider the xtz.
Hope this helps