Thank you very much all, and apologies for incorrect use of film speed. But thankfully some of you have understood me
I understand speed is measured for little density change in shadow areas and some developers give better results on those areas.

Purpose of my question is because I’m asked to write a post for reader in Turkey about technical bits of film, chemistry and everything about it. Due to currency economic situation, they don’t have a chance to try all the different developers and I got the task at least to show them different developers as well. Otherwise I’m all the way HP5, F100, Rodinal and XTOL guy and tried DDX in the past so I have a good selection of comparative negatives.