I remember having read that there is a "gamma infinity" for each film/developer combination which will not change any more after a specific development time. So some films might end up w/o any midtones at all while others will just be pretty contrasty.(posted 8779 days ago)If you want pure b&w contrast, you might use repro film (such as Macophot Ort 25) or Kodak Tchnical Pan, developed for a long time in a suitable developer. But I think you will have more room for creative experiment when starting from conventional negatives. A full-tone negative gives you all the choice to eliminate or extract specific tones. If, otoh, the film is developed to pure b&w contrast, you have to decide on where to draw the line between the two when you shoot.