I need to buy a cutter for my cnc build and I will be mainly cutting plastics- especially polystyrene, some acrylic, nylon, pe, etc. I would also like to be able to cut aluminum and sometimes wood. What is the best spindle speed to cut the plastics mentioned above?

I am looking to buy a variable speed router from Sears that runs from 12,000 to 25000 rpm- is this too fast for plastic?