Quite low spindle speeds, I think, so you don't melt the material.
Try out on some scraps. You will know if spindle is too fast.
Plastic will melt into the cutter flutes and clog up things.
Make sure test pass not too deep, as you may start pushing a solid non cutting cutter as a plough.
Keep PLENTY of air so no swarf gets eaten by the leading edge of the cut.
You can push fairly amazing feed rates once you get it right.