This weekend I took nearly 5,000 shots with my D5100 at a MotoCross Race. My keeper rate was dismal shooting single point . The camera and AF-S 28-300 lens combo were having trouble locking on in time for the shot. I am spoiled by the >95% rate of the D3. It had become too heavy for me to shoot all day, so I sold both bodies.
I am hoping the D800 is much better on both counts. What I have not decided is whether to shoot medium JPEGs, 4x5, or DX mode at Events. Portrait, weddings, and Landscape work would be shot FullFrame.