Thomson’s industrial linear actuators use single-speed motors that output a constant torque when energized. The linear velocity generated by this torque will vary somewhat based on the applied load. Our catalog notes both no-load and full-load speeds and, in most cases, includes a chart detailing Speed vs. Load.
The best option for AC speed control, however, is moving to Thomson’s precision linear actuator line.  The PC-series and T-series actuators ship motorless. This allows you to select a motor based on your individual application requirements, including speed variability.  Alternately, the ECT-line has a variety of AC servo-driven actuators and 3 phase AC induction motors which are speed controllable.