I would test on some scrap pieces. Too slow cut speed or too high spindle RPM will create excessive hear and melting problems. The bit choice is important with plastics and foams. For HPDE use an O flute, single flute, or other such high helix upcut bit made for plastics. More passes will allow you to cut faster at higher RPMs and generally give you a better edge finish. Specific speed and feeds depends on your tables capabilities and what bit.