I would personally stick with the carpet. If you get the bunks wet enough and the trailer at the proper depth/angle you should not have any issues with loading or unloading the boat. You mention you are looking for the slickest material out there, is it due to issues with loading and unloading? There are strips you can put down on top of the bunks that make it really slippery and the manufacturer makes mention to use caution as they work quite well I suppose. I use bunks on all the trailers I have without anything to make it slippery without issues.
'86 Comp TS6M - Reborn 2016
Riding a HO Sports CX Ski