Well, like John said, the FZ6R is plenty fast for street riding; but, I had to know what all the fuss was about with SS, and I had to own one to learn for myself, I am kinda that way with everything; well, now I know, yes a 600SS is faster than the FZ6R, but that power is up top and it is a very energetic experience, definitely exhilarating, but its a lot of energy being transmitted through you above 10K RPM, I just found out at my last service that there are 2 fuel maps on the gixxer, and they cross over, so the top end becomes fully onto this other map and you can feel the bike become very manic above 10K (where the last 30hp reside).
Like I said its exciting, but its a lot of energy, not exactly a relaxed situation. So, I would spend a lot of time thinking about whether you want more HP on the next bike, or more torque (e.g. FZ8 or FZ1). That said, a 600ss keeps you interested cause you are challenged by it, kinda like trying to ride a wild horse, but sometimes you just wish you had one that wasn't so wild.