I spent about a week calibrating Ilford Delta100 in a couple different developers. I have only ever shot it on 35mm on a few rare occasions. I ultimately decided to stay with Kodak TMAX 100 for both 35mm as well as medium format applications. The Delta 100 was a fantastic film and a worthy competitor to TMAX 100. My decision to stay with TMAX 100 over the Ilford film was purely subjective, I had no technical issues with TMAX 100 as so many others do and I happened to like way TMAX 100 spectral sensitivity rendered caucasian skin tones a little bit better when shooting it unfiltered. In PMK there is virtually no grain, for those of you shooting detailed subjects on 35mm it is fabulous. In medium format it would easily fool you into thinking it was on 4x5 large format blown up to 11x14.
If you like slightly darker caucasian skin, shoot in smaller formats, want something with no grain, and you don't use filters it may be the film for you. I honestly have no idea why someone would shoot FP4 instead of this stuff.
Sample image is a strait 4000 DPI scan of a 35mm negative during one of my calibration tests, shot with a Leica M6 and 50mm Summicron, hand held. My EI for this film in PMK turned out to be ISO 80. No sharpening as usual.