Since the difference between the Z and ZL is one is water resistance and the other has a camera button, but everything is the same I don't see the need for a different forum.
ZL has smaller chassis
ZL supports LTE Band 4 (T-Mobile) and 17 (AT&T) while the Z doesn't support either
ZL is available, unlocked, in the US through Sony's US website later this month. Z will not be sold in the US
I'm seem to be posting just as often to Z segment or perhaps even more than in this segment. The differences are very minor overall, and Sony's UI is consistent over these handset.