I would second Henry's suggestion. I have found that XTOL yields noticeably higher film speed than most other developers with Delta 100 film (I haven’t tried Delta 400). Anchell and Troop classify XTOL as a speed increasing developer in the "Film Developing Cookbook,” (1998 Focal Press, page 5). Using XTOL 1:2 dilution (or higher) ensures that it will yield sharp negatives without increasing grain. If you want even less apparent grain (with some loss in sharpness), try XTOL straight.(posted 8223 days ago)