I don't have a lot of experience cutting plastic and I've only tried normal 2 flute 6mm cutters on a 1.5kw spindle. Acrylic is relatively easy to cut but some of the softer varieties like HDPE can be difficult to get a good surface finish. One has to keep the rpm surprisingly low not to melt the cut and ruin the piece. Maybe those expensive specialized single flute cutters works the magic on the softer plastic? Not sure about the power requirement but I did not get the impression that one needs a big amount of power but considering the relatively low rpms I would not go to small on the spindle.