Woah. Even so, 1/2000 or 1/4000 is a little over the top. The only options you have now is to shoot using a fast tele lens at a large aperture (so more light can get in), or bump up the iso to get a decent exposure for shutter speeds between 1/500 to 1/1000. Though you would have to sacrifice some image quality to get a sharp shot.. If all else fails, you could try panning, though the resulting effect is quite different.