Upload & Sell: Off
Add one more to the list of those who found the 1D Mark III to be a significant improvement over the 1D Mark II or 1D Mark IIN.
I'm one of those who found the 1D Mark III AF to be better for shooting action than the that of the 1D Mark II or N, and that was even before the 1D Mark III AF fixes.
Further the increase, even if not large, from 8 to 10 MP was noticeable to me, and I found the 1D Mark III files to be more pleasing to the eye than those of the 1D Mark II or 1D Mark IIN. There is also a noticeable improvement in high ISO capability. Even if the 1D Mark III screen is one with relatively low resolution, the increase in size was a nice improvement, and the changes in the user interface and the weight reduction of the 1D Mark III mentioned by others made the camera, to me, more user friendly.
While the 1D Mark IIN was a superb camera in its day, it is now approaching 7 1/2 years since its release, and its technology is starting to show its age. Also note that Canon already announced a while back that it is no longer servicing the 1D Mark II, and I would expect that they will be making a similar announcement about the 1D Mark IIN in the relatively near future. While I'm sure that you would still be able to get one serviced at an independent shop if it has access to parts, a camera of that age is likely to have lots of clicks on the shutter, and the likelihood of the need for a shutter replacement or other repairs is higher than it would be for a newer body.
If given the choice to spend a few hundred dollars more for a 1D Mark III, going in that direction would be an easy choice for me.