Of course now I think the choice for me, between the D4 and the D800 is tougher, since their high ISO/low noise characteristics are so close. (LOL)
If I only did sports or wildlife (flying birds) moving larger animals, etc. the choice would be an easy D4. If I only did travel, architecture, macro, weddings, the choice would be an easy D800. Unfortunately for me, or fortunately as it's lots of fun, I do travel, architecture, events, news, only an occasional wedding as I really like to avoid them, and all kinds of wildlife, with some sports.
This is getting tough and I've got to make a decision soon, as if I'm going for the D800 (can't justify both right now) I want to cancel the D4 order sooner than later, and definitely before it's shipped to me.