The speed capabilities of our industrial actuators vary depending on the model. Our catalog contains data sheets for each actuator, including the speed vs. load curves.  To a limited extent, you can reduce the speed of an actuator at a given load by reducing the voltage to the actuator. However, if the voltage is reduced too far you will limit the current to the actuator, causing the unit to stall. Most of our industrial actuator units will function within +/- 10% of their rated input voltage.