I agree with David and I think what is seldom appreciated is
that:  - spectral (wavelength) sensitivity can be a major player
in tonal separation and contrast  - stated filter factors are
quite arbitrary around the edges of the sensitivity spectrum;
you have to convolve the lighting spectrum (~colour temp) with
the film sensitivity spectrum to get reliable numbers  - no
matter what the manufacturer's stated toe and knee look like,
you don't know from the H&D curves what actual highlight and
shadow curves you're going to get unless you again consider the
actual lighting spectrum used for your shot and the film
sensitivity spectrum. A pan film can deliver an image that is
tonally contrasty or it can be blah flat... with the same
developer and the same dilution and exposure time and
everything, just by shooting through a colour filter. Extreme
example: rollei R3 unfiltered, Rollei R3 red filtered. Please
ignore the clouds in the sky, I am not talking so much about the
dehazing effect of a red filter, but rather