I have thoroughly enjoyed reading this thread to this point. Alas not in my budget so why worry, because it is fun.
It has the same shutter as the D700 which is loud, and for one of my ventures unacceptable, which is unfortunate.
Part of the announcement over the loud speaker is, ask the photographer to stand down during your test if your horse has an issue with cameras. Some of them do and it is usually the click of the shutter.
I have found shooting Dressage as a professional, as well as other sports on a casual basis, it is all about learning the sport and timing and has absolutely nothing to do with frames per second.
I know others have stated the above about timing your shots but I wanted to repeat it. In dressage you get one click and only one click. I get invited back to shoot events by following the rules and not machine gunning my shots taking a serious risk of spooking a horse.
And no a D3, D3s or D4 is not in my budget so please don't go to the quiet shutter mode of these fine bodies.
And yes I could use a higher ISO in some indoor arenas but the D700 does just fine for now.