For Delrin I use 400 SFPM for HSS end mills and 800 SFPM for carbide end mills. 150 SFPM for drilling. If you are using a CNC control, if it has G73 pecking cycle, use it to break the chips. Using a standard G81 cycle the chips can be stringy and stick to the drill.
I don't know about the High Molecular Weight Polyethylene, I would try the above though.
As for chip loads I use the same as I would for aluminum. Without the concern for horsepower or breaking tools. For end mills .010 x the dia x number of flutes x the RPM. For finish .016 x sqr(dia) x RPM (minimum finish feed.) For end cuts .0095 x RPM. For drills .020 x dia x RPM.
Safety - Quality - Production.