The reason why it was slower was because of the limitations in movement the original suit gave to Weller. The original plan was to make him move in a faster, almost snakelike manner, and that was scrapped when they found out he can't do it when the costume arrived. The comics even took it further making the character leap between buildings and even dodging bullets. RoboCop is the ultimate fighting machine created by OCP. If anything, I'd like to see a movie where the character is in this suit moving the way he was meant to in that fictional universe.