I had a D7000 and switched over to a D700, and it did, comparatively, feel like a tank. However, I'd become so used to the D7000's button layout and menu structure that I found the D700 somewhat frustrating (totally a me issue). So I returned the D700 and got a D600 and have loved using it. I say all if this as a roundabout way of asking the OP "what body are you currently using?" I'd also ask whether you're using the camera for indoor or outdoor equestrian photography. Both cameras are great (though Thom Hogan does say the D600 is an upgrade from the D700), and I don't think you could go wrong with either.