It may be possible to set the speed of the Makita trim router via some electronic box but I suspect not. The usual route for speed control is to exchange your trim router for a spindle that is controlled by a VFD. Then commands can be sent to the spindle that will be speed commands. The settings you make in your CAM software are important in terms of how the cutting bit is applied to the workpiece.
Step down = how big a bite the tool will take at each complete pass (on a single level) of the tool path.
Stepover = how much of the tool diameter (reflected by the cutter moving sideways) on its next pass at the same height so that the total workpiece is milled.
Feed speed = this parameter determines how fast the cutter is pushed through the workpiece, bearing it in mind that it creates a lateral force. Too much feed speed will break the cutter or damage the workpiece.
Plunge speed = the amount of time taken for the cutter to move down to its next stepdown position on a subsequent pass. A hard wood or metal will break the cutter if you force it too fast or too far into the workpiece.
That’s it. You can set a speed for the router but unless you have a spindle and are hooked into the control box, the software which creates the toolpaths (CAM software) will have no effect on the speed of rotation of the Makita Trim Router.
gSender is not CAM software but control software and its job is to pass the GCode created by the CAM software to the hardware controller of your CNC machine. While GCode can be hand edited and speed of the spindle is one of the parameters which can be adjusted, it is not a task which is usually done at the control software level.
I recently added a document which demonstrates a set of speeds for my own Makita router. These are averaged values taken 5 times for every reading and it may assist you.
EDIT: typos and grammar and URL addition.