He's hitting 50-70% with the D600, D800, and D4 and the updated AF system.
Dave's suggestions are right on target. The center sensor is much better for this kind of image. Also its good to fire off a series of images as the camera will refine AF on each subsequent shot. This kind of image takes a lot of practice and even then has a low success rate. Keep the shutter speed very high to freeze motion. Also be sure to try some intentionally blurred images with slow shutter speeds.