I have a D700 and I'm facing a similar issue. I've got a preorder on the D4 but am now questioning the wisdom of that. The D800 is very tempting, too. I'm not a fan of the extra pixels but the rest of the package seems very good. Honestly, the more I ponder this question the more I think that upgrading the camera won't improve my photography all that much given that I'm totally an amateur with limited time to photograph. I still see amazing shots done on a D200 that I haven't been able to surpass with my D700. That tells me my skills are what's holding me back more than my equipment.
Doesn't answer your question exactly but maybe gives you a different way of looking at it.