I've got a ZX6R shock. Compared to the stock the spring is about the same - but the damping is better. It's worth the $50 as long as you weight 240 or less (I'm 240). Unfortunately I want more spring because I usually have a passenger. I might celebrate my new job with a Penske double clicker. I have 1kg springs up front and 15wt oil. I have the preload set with only 2 ridges showing - so I'm glad I got the 1kg instead of the .95kg which other 240lb riders are using.
The 05 ZX6R shock raises the rear about a half an inch - which I like also. I heard the ZX10 shock spring rate is lower - but Marthy can tell you more about it than I can.
I've been watching for a ZX6RR shock for about a year now... They are out there - but they go fast.