Thanks folks.
The last shot was taken in the indoor arena which is an absolute bugger of a place as it the jumping takes place under cover, but as there are no walls the background is always brilliant sunshine and with horses jumping flash is not very clever.. I tried that shot at 1250 ISO and then cropped and removed some of the noise with Noise Ninja.
I'm happy with the first 2. Taken in much better conditions. A friend had sold her horse recently and was keen to get a few shots of it jumping. I was only there for 30 minutes most of which was spent gas bagging so I only took a few shots. Amazingly, the 2nd shot of the grey was her horse. I had no idea. What are the odds of that with over 200 horses competing.