I also have this issue with stock suspension during a track day. Already max out the rear suspension setting but still feel like a small boat hit by an ocean wave. But with this ZX10 shock, it feels silky smooth when taking a highspeed corner.i also ride track days with stock suspension ( have adjust it ) but on high speed ( 2 -3 gear ) bike starts to shaking rear end , like ship swimming in ocean . it's very scary . did you have same problems with stock suspension ??