There is very little difference in AF speed between the D3, D700, D800 or even the D2 series bodies. AF focusing speed is much more obvious between lenses then between bodies. I tried my 2-ring AF 80-200mm f2.8 lens on the bodies mentioned above and couldn't say one body was faster than another. I had to go to a D1X and D1H body to see a difference. These older bodies seem to have a higher torque motor which produce a fast AF but have an abrupt stopping action that causes a small bounce very similar to the powerful motor in the F5. The newer bodies like the D3, D700 and D800 have a smoother AF action but not slower. It certainly isn't a performance parameter I'd consider when getting a new body.