I use a D800 for Motor Racing in the UK, AFC a must 1/640 or faster a must for sharp images if using a 70-200 2.8 at f6.3 (sweet spot), ISO 400 and up to 1600 no trouble at all, use 9 point array rather than 3D (it gets confused if more than 2 people are incoming). 9 point will allow the D800 to focus very quickly but use the AF on button as soon as you start tracking. I do not spay and pray I still take a picture as if I had film stock in. I get too many keepers compared to my D300s, I tend to use the focus tag in View NX to dump any un-sharp pictures and then load to lightroom as NEFs. Enjoy the D800, it is in my opinion, the best camera on the market today.