I once did a very simple test, where I set up a Pentax 35mm camera with a standard 55mm lens, with a shade. I used a tripod and cable release, put Tri-X in the camera and shot a scene of a railroad yard with train cars and grain silos in a medium contrast setting. Just to make sure I wasn't using anything exotic I used something like D76 or Ilfotec DD-X to process the film, and then I made 16x20 prints just to see how good I thought it looked. I liked it so much that I decided to make a whole series like that, and I used TMax 400, Tri-X 400, and some HP5+ to make all the exposures. It turned into a nice series of photographs, the final prints were printed to 8x18" size, and the people that saw the prints didn't exactly comment on 'grain structure'. Attached is one of the photographs of the series called 'Never Sleeps'.
I wonder what meaningful differences other people see between the two films, something that truly matters to the outcome of their prints.