As far as TRUE positional feedback you would need linear scales on the ways. What Mariss may or may not have told you, there is a partial feedback when using servos and his G320/340 drives. I really like knowing that I can't loose steps with the servo system if I push it just a little too much. If the steps get too far behind, the drive will fault. With a stepper setup you will loose steps and not know until you go an measure your part!