i have 07 zx10, and my stock sprocket is 17 in front, and i dropped to a 16. I have super fast acceleration, if you can keep front end down and it puts speedo off a good bit. I bought a speedo healer and put it on and bike reads dead on with a gps now. I guess it takes about 5-10 mph off top end though. But i ride to work mostly and just get out on weekends so, i didnt miss top end too much.
07 zx10- -1, speedohealer, GiPro with TRE, Leo Vince Carbon SBK slip on, Lots of Black spikes, Candy Blue