Here's a match up between the 24mp D3X and 21mp 1DsMkIII. Basically the canon wins image quality (but not by much) and the D3X wins for better and faster auto focus and for ergonomics.
Actually in the end they kinda don't like either camera because they don't bring anything new to the table other than big pixels. They say just stick to your current D3 or 1DmkIII gear. They also don't think these cameras give medium format too much to worry about.
Interesting read nonetheless.(lots of picture peeping)
http://www.h2hreviews.com/article/Head-2-Head-Review-Nikon-D3x-vs-Canon-EOS-1Ds-Mark-III/Introduction-The-Matchup.html
(Thanks canonrumors - uh, um I accidentally ended up over their somehow :)
