I am pretty sure the ZX6R was 636cc and the ZX6RR was a true 600. They would have to keep at least one at 600 or under to be legal for competition.
So yes, the '05 and '06 ZX6R are all 636, but there is another model that is really 600 (or probably just under).
If I'm wrong, I'm pretty sure someone will correct me.
I hope that helped.
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