I think to purchase SmoothStepper. And I need some information. Does SS update motion with rate more than Mach3 can do (10Hz)? When not, how it do motion more smooth?

The SmoothStepper can generate a pulse stream up to 2 MhZ (the SmoothStepper output). Mach sends the SmoothStepper a series of commanded positions, the SmoothStepper buffers them and then generates the needed pulse train to move your machine. You can adjust the SmoothSteppers velocity update rate to match the requirements of your needs as well.