The question was never the relation to fstop to iso, it was iso to a cloudy day. In which case there is none.
Also fun fact if you are real persistant about having less grain to minimize noise. ISO that are divisible to 160 produces less grain. In fact studies have shown that 160, 320 and 640 have less grain than 100.
I just have a question though more related to your thinking process which is very peculiar.
You are saying that you adjust the shutter first (your comment about not compromising shutter speed) then you adjust ISO then F-Stop?
I’m not saying its bad. It’s just unique. Definitely different from the way some people shoot. Usually it’s either F-Stop or Iso first then shutter is adjustable.