I've not used D-23 with medium or low-speed films, so this experience may not apply. I have used it diluted 1:3 and 1:4 with 35 mm TriX shot at ISO 400. Using a semi-stand agitation - first 30 seconds constant and then six inversions every five minutes, I wet print grade 3 with 1:3 done 20 minutes at 68 degrees f. With 1:4, the prints were consistent grade 4 but with greater definition. That said, neither gives the same definition as two-bath D-23 as per Barry Thornton.