Thomas, you're right of course - film speed, (shadow density) is essentially inherent in the film, not in the developer. In fact I've used Rodinal at 1+150, (20 deg. C, 7 min) for 4x5 Tech Pan. It's just that I find my prints appear, (and it may be just appear) sharper with higher dilutions and longer dev. times - even in the same developer.