I would shoot at the D800's native 36MP format and use sneaker zoom to get a little closer to the subject.
If you can't get any closer, the D800 gives you excellent cropping capability. Just crop the subject out of the middle of the sensor and you'll have an image equivalent to the D7000 without switching to DX mode.
You aren't losing anything over shooting with the D7000 except for a larger image showing in the viewfinder. The D800's massive resolution allows you to crop significantly and maintain detail.
Later, sell your house and buy a 600mm f/4 Nikkor!
============================================== Darrell Young (DigitalDarrell) www.pictureandpen.com "Better too many words than not enough understanding." ==============================================