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 how the wood and grass tones are rendered, which has nothing to do with haze or Rayleigh scattering.

David I don't know if this is what you meant, and I don't mean to put words in your mouth, but when you said tmax's response is too linear for your taste, I took that to mean too linear in overall wavelength sensitivity, which is an issue I see in these R3 test shots. My feeling is that tones simply don't separate well at all unless a filter is deployed.

If a filter selects out that wavelength range that coincides with a big change in the derivative of the wavelength sensitivity curve, then, voila, more tonal contrast. I suppose this is because small changes in the tone/colour across the subject give rise to large changes in actual density in the neg. Requires more thought.

I seem to have more success generating tonal interest and good separation with traditional-grained films, and the tones clump up for me with tmax and the deltas. Maybe it's just me :s