ISO Speed / Shutter Speed

Tonight I thought i would compare ISO speed with shutter speed. I took 9 pictures of the moon. There were 3 different ISO speeds: 200, 400, 800 and 3 different shutter speeds: 1/80, 1/100, 1/125 seconds. From the picture it seems thats the best result came with the lowest ISO and a corresponding shutter that neither over or under exposed the moon.

All pictures were taken with a 270mm lens at f6.3