I took some shots at the Sydney Triathlon today, and I played with different settings.
It seems to be there are some advantages in shooting at a higher f stop and lower shutter speed, which may negate some of the perceived advantages of "fast glass."
For example, this photo is taken at 135mm f8 1/125 (no SR - so the shutter speed was marginal):
It seems to be better at conveying motion (because of the motion blur of the wheels and the background) than this one taken at f5.6 1/750:
What do people think?
Another comparison - runners at f8 1/125 (note motion blur around arms and legs):
Compared to a sharp, but fairly static image at 1/750:
On the other hand, I quite like this one, even though it's rather static: