2mm vs 3.17mm thickness of flooring. What's the difference?

There is no difference in the performance specification between the 2 mm and 3.17 mm thickness tile.  They are manufactured the same way.  The biggest difference is telegraphing subfloor imperfections.  My rule of thumb is 2 mm should only be used for new construction.  The 3.17 mm should be used for remodels.