Canon has published EOS 1D MK IV white paper. Here is the pdf
In the AF section there is one plot that provides quantitative data for AI-servo tracking performance, comparing this data what that of 1DMKIII it seems that AF speed of the new camera is identical to the old one, the new improvements are hopefully in AF stability and tracking consistency.
http://www.stanford.edu/%7Eahazeghi/...ck%20speed.jpg
