Originally posted by Elisha I love this lens for headshots and close-ups of the horses working but for full body shots I'm pretty confident at this point that I need something faster. :|
Are most of your shots handheld?
If so, be aware that weight can present a serious issue with "fast" long lenses.
I think in terms of f/2.8 lenses, a 200mm prime or 210mm zoom is probably the limit for hand holding during an event or a session longer than 10 minutes.
These lenses weigh about 3 pounds, which doesn't sound like much, but it's a lot to be holding steady for any length of time.
A 300mm f/2.8 lens is going to weigh around 5 pounds, which will wear you out much faster.
At 300mm you might need to look for an f/4 lens, which is back down to about 3 pounds.
None of those are really cheap, but you can save up for them. If you're getting paid work, it should only take a few jobs to cover the cost of a used 700-200/2.8 or 300/4.
Has it been suggested yet in this thread that you could try renting? There are several good lens rental places on the internet. LensRentals, BorrowLenses, CameraLensRental, etc. (I've never used any of these places, I've only read other people's experiences).
This would let you try out several things, and see what will work well for your specific situation. It will, unfortunately, cost as much as "cheap" lens to rent a nice one.