This sort of thing really depends on the application, and the nice feature provided with the new "force" property is that you can actually distinguish between a "whole finger pad" light touch, and a "thin, firm, almost just the finger nail" hard touch, and most things in betwee.
I don't think is gonna be consistent among different fingers/people, sadly. but synaptic did pressure sensitivity on contact area long ago, wouldn't be surprised if they got some nice normalization heuristic already going.
edit this is funny coincidence: the dev guide for synaptic says 255 level but better badn in 7 levels at most