Pixel fixation of the worst kind!
Seriously, I appreciate the thread, gentlemen.
My take: at 800 ISO it's a tossup. At 1250, the 5D boasts clearly less noise at the pixel fixation level (I have yet to see one of my clients smash his nose against one of my images in an effort to get the eyes close enough discern noise at this level) but no more noticable detail.
Given these results, I would not suggest that any current 1DS owners "upgrade" to the 5D.