Have you contacted Rockwell Automation about this? They might be the best source of information, or can at least point you in a good direction...
Looking at the datasheets, I get the feeling that "frequency" is more a matter of what the upper and lower bounds could be, based on the mass being moved, and the acceleration needed. I am sure all the information needed to calculate these upper and lower bounds are in the datasheet, but I don't know how you calculate it. Anything in-between those bounds would cause the moving coil assembly to move (for that mass - things change if the mass changes, of course). Raise the frequency, and the coil assembly and mass moves faster (while likely consuming more current - these things appear to take a LOT of current!).
If you note in the datasheet, though, it says that you need to provide an active feedback servo control to these motors to get them to operate properly. Think of it this way: In order to be able to move from point A to point B along the track, your controller must do the following:
1) Accelerate (ramp up) the frequency to get the coil and mass moving.
2) Hold that frequency until you approach point B.
3) Decelerate (ramp down) the frequency as the coil and mass approached point B.
4) This step is potentially optional: Apply a direct current (or some out-of-phase) holding current to the coils to keep it stationary at point B.
Step 4 could be automatically accomplished with a proper servo control mechanism (likely PID based - if the mass overshoots, it would be moved back; if the mass is moved by an external force, it would be moved back). This servo control feedback loop could be accomplished in numerous ways, depending on the accuracy and quickness of response needed (and how much money you're willing to spend); basically, it is a sensor that can somehow measure where along the track the coil and mass are. This information would be fed back to the controller, which using its PID loop would determine what the frequency is needed to apply to the coil to move it to the position commanded.
You're talking about a fairly complex system here, it seems; the linear motor is one part, you need a controller with a PID loop, a servomechanism feedback sensor system, and to top it all off, you need a controller that can handle a lot of current at fairly high voltages (meaning if you design it wrong, you might get an impromptu fireworks show instead!).
Once again, though, I want to state that I have -zero- experience with these devices; the above is pure speculation on my part as to how these things work based on my little knowledge of them in general, and the datasheet you have provided for your particular motor, coupled with what I know of servomechanisms (which isn't that great, either)...
Seek the advice of experts...hopefully some will post here (but since this thread has been running a while, and none have showed up - contacting RA and asking them for advice or outside services might be your best bet).