Thanks, I just tried some cutting again with the suggested feeds and speeds of G-Wizard and it doesn't melt the plastic as I thought it might. I guess the key is getting enough chip-load not to cause rubbing.

I'm cutting 8mm sheet, so I did multiple 3mm pass' at first with a 6mm cutter and then did a finishing pass at full depth removing 0.5mm of material. The end result is very good but there are still some very slight snipe marks. I need to sand and buff it afterwards for a real smooth finish. I tried flame polishing it with a butane pen torch but I think the flame is not hot enough as it looks a little patchy.