I wanted to see how the Sigma 150-500mm lens functioned for sports with AI servo focusing with my 5D Mark III. I also wasn't in the mood to process a lot of RAW images so I set the camera to save both RAW and JPG files. I won't do that again.
First, the JPG's were useless. The files needed white balance correction and highlight lowering and/or shadow raising. Second, saving files in both formats slowed down the camera and shortened the burst duration. Live and learn.
The lens actually performed decently and, in full sunlight, I wouldn't hesitate to use it again for field sports. For night action I would need to use my 200mm f/2.8L lens with my crop sensor EOS 7D.
Here are some samples. The full gallery can be viewed at http://trulandphoto.zenfolio.com/wickskidmore. 500mm is nice. The shot showing the goal posts is from about 10 yards behind the opposite goal line and is not cropped.