Twister

The EXIF data on your image shows 1/500 (good! only way to freeze that action), ISO 320 (tolerable for noise, good), and f/5. Hmmm... f/5. I'm not sure what lens you're using on your 5D, but if you can open it up to, say, f/2.8, you'll accomplish a few things.

First, you can thereby raise that shutter speed even more, and preserve more of that wild detail. With things whipping around like that, there IS a difference between 1/500 and 1/1000.

Second, you could lower the ISO, thus reducing noise. But at 320, you're pretty much fine anyway.

Third, you'll get a more shallow depth of field. That could be VERY useful in a scene like this, because if you can get all of that background business even just a little out of focus, it will help isolate the horse and rider. Of course, in this shot, the guys watching are an important part of the composition... so that's all very subjective. Great subject matter - do more!