It was when I started printing in the darkroom and found my size, 11x14, that I really started "findng" my limits for certain 35mm films.
What I've now found, and this is just for me, is that HP5's and Tri-X's grain can really start competing with small but important details on a significant number of shots at this size. Delta 400's grain generally doesn't seem to interfere so much.
Delta 100 though makes a significant improvement in the fine details and I'm finding that I can shoot it just about anywhere and anytime in almost any situation that I used to think I needed a 400 speed film.
My only real struggle with Delta 100 is the contrast, I know that's a solvable problem, but it is really tough to get excited about that work when that darn old school FP4 shoots so easy and nice. So easy that I just bought another 100 feet plus 10 rolls of 120.
Many people do very well with one film, and Tri-X is a nice one, but you'll never know how the others might fit until you try.