OP,
Stop looking for a bull$hit S mode that isn't going to do anything noticeably different. The Z D mode > any sedan/coupe (NON-sports car) S mode. Go drive a TDI or G37 if you want S mode. It's just marketing bs. Of course there are differences, but don't think a G37 in S mode is going to shift better or faster than the Z in D mode.
The Z D mode learns how you are driving and adjusts to compensate. If you want it to shift harder, then you have to drive it harder. I believe there are some tuning options for the 7AT as well.
The 7AT on the 370Z is a pretty phenomenal transmission, especially considering it's age (FP, don't you dare quote this in the Auto vs Manual thread
). And I drive the 6MT. I agree with SouthArk in that if you don't like it, you should probably look at a different vehicle