DxOMark has tested the D800 and it has scored the highest score ever by any camera including MF cameras, and higher by a fair margin, on DxOMarks scroing of 95!! Yes, I know we can argue the merits, or lack of, of DxOMark, but even so, that's a very impressive result and says much about the D800's new sensor.
http://www.dxomark.com/index.php/Pub...or-performance