What is the best iso and shutter speed for shooting runners on cloudy days?

Generally, runners don't run very fast, so a shutter of 1/50~ 1/250 is enough.

Cloudy days also glow, unlike cloudy days, depending on the light intensity, 100-200iso is enough.

Try to use a large aperture and less telephoto (if the machine is not very good), because the aperture at the telephoto end is not adjusted much.