Well, the slope of the curve determines overall negative contrast, the toe determines film speed / shadow detail, and the shoulder (and its slope) determines highlight contrast and density.

The most important thing for the mid-tones is to make sure you have enough exposure in your negative to well define all those tones that you find important. Then develop the film so that they print the way you want them to. Keep in mind that different papers (and paper developers) exhibit different tonality too, so it's best to keep those constant.

My own method is to target Grade 2 to Grade 3, printing on Ilford MGIV matte fiber using replenished Ethol LPD. That requires a negative of high contrast in order to make the blacks convincing without making the rest of the tone spectrum muddy and flat. I don't have equipment to measure any of it, just a method that I work with to get what I want. I always target the paper with everything that I do. That's where it all begins.