I believe when pulleys are used it is to reduce the speed and gain torque. Maybe if you are cutting foam. Are you running Mach 3? Is it set for 25Hz? Increase the Hz and it will increase the speed the way I understand it. Is it too slow now? I dont think a pulley system introduces backlash any more than any other system. Any play will cause backlash whether it is direct, gear or belt driven.