I have seen one or two reviewers that claim the comfort seat is thicker but squishier and they didn't like it due to you move around too much on it.
I hated the seat on my Versys so I bought a rubber backed Alaska Leather pillion sheepskin (in black) seat cover. It did the trick, much more comfortable on long rides. Although IMO a sheepskin seat cover, though it looked OK on a Versys, will totally ruin the look of the high tech z900.