I think you'd have to be an absolute top player to notice a difference between 2 mm and Max. Except with one of those racket-measuring thingies of course.
One of the "organisers" at my club's old fogey sessions - I put that in quotes as he could barely organise a visit to the adjacent supermarket - insists, purely on visual inspection, that my Aurus rubbers can't possibly be 2.1mm sponge, despite the fact thay they came out of a "2.1" packet. I have learnt to ignore this sort of nonsense.....