It really all depends on which material you are using. Check out the material guidelines for individual material tolerances. The polished material is intended to only take of the extended ridges so not much at all. Your friendly neighborhood Moderman
If you follow the design rules for WSF, they will be the same for Polished - as both parts will undergo the same polishing process so the minor surface treatment they undergo will be the same for both.
Hence, if they fit together before polishing, they will fit together afterwards.Shapeways Community Manager