Suggest someone rent or borrow each camera. I did a 2 hour shoot with the S. AND I have walked around for street shooting with the Z for 4-5 hours on more than one occasion.FWIW, I do not find the handling of the 645Z to be bad. I know people rave about the lovely S and it does look svelte and gorgeous, but seriously, the 645Z is one of the best handling cameras I have ever used. Its an absolute joy to shoot hand held, altho it gets heavy with the massive 28-45.Weight aside, its one heck of a machine than shows just how well a tool can be designed with the user in mind.
My reaction-after 2 hours with the S, my wrist hurt like heck. After 4 hours with the Z and heavy 28-45 lens, my wrist was just fine.
For me, I find the Z just fine for walking around. I cannot say I find the S best suited for that type of work.
Perhaps it has been done, but also suggest one read MR's Lula reviews of each camera, if his comments help (Z-Sept 2014, S-October 2015) There are few cameras Reichmann has not handled and his insights leave much food for thought.