It's all what the situation calls for... Just yesterday I captured a still shot of a flower in a field at 1/6400. The very high speed was necessary because it was bright midday sun, and I wanted to isolate the flower from the background so I shot at f/1.4. Same day, same lighting conditions, on other shots I was going as slow as 1/200. All depends on what's needed, you're given 3 exposure variables and you can do what you want with them. : )