Of course it depends on the lighting and the camera itself, but I always try to keep my ISO as low as possible to get as "grainless" pics as possible. Those are some very nice shots GarryHarris. Although the ISO could have been a little bit lower (only my personal opinion, since I don't know what the lighting was at that stage) - it still is great shots.

I usually try to keep my ISO in the range 100-400 when taking shots like that outside. Getting used to a new lens also is a bit tricky. Here are some photos of the first Model Airshow I went to after getting my new Sigma lens. Also the day my AF failed.

*I adjusted the images to get them on here - hope it didn't lose some quality*