Cutting force is tricky - it would probably be much easier to get a good answer by building a test rig to measure the force directly on your material using whatever cutter / spindle / cutting parameters you plan on using on your machine. You could get this in various ways such as using a force sensor or measuring acceleration or velocity using a known applied force (such a hanging mass). Doing this, you could find the force required to cut your material at various speeds / cutting parameters. Then you could design your motion system to provide that force in addition to the force required to accelerate the moving mass of your machine. I want to do this before I rebuild my current router so I have some real targets to design around.