Seem to recall that denier has more to do with the weight, rather than the size of fibers. Franco has the definition - maybe he will post it again.
From my experience, the Cordura will be more abrasion resistant, as it is made from fibers tougher than most other nylons, and the material between many of the spectra and dyneema gridstops is not Cordura nylon. There are balloon cloth nylons that are very tough, but I have no reason to believe they are used on any of the dyneema gridstops.
However, every weight of Cordura I've used, from silnylon up to 10 oz., has not had a very good coating. Waterproofing was no better than average, and the coatings wore off faster than those on other nylons with high quality coatings.
Pick your poison.
Or for a pack bottom, bond in a high hydrostatic head material. For the packs I'm working on now, the bottoms are lined with Thru-Hiker's silnylon, sewn and bonded in place. But I've given up bathtub pack bottoms, as I take much better care of my lightweight gear than before, and the main pack fabrics when well sealed are water resistant enough to keep water out if the pack somehow gets set down in water; like slipping and falling when fording a stream, for example.