Thanks for your interest in DxOMark.
The scores are updated, there was a slight mistake for D800 (which scores a Sharpness of 14 Mpix too).
It is very common for such lens (super zoom) that Nikon D800 and Nikon D600 perform similar Sharpness performance.
Super zoom are not the sharpest lens available and most of them do not provide enough of sharpness to make a clear difference between the 36 and the 24 Mpix sensors.
The Dxomark score remains the same: 19. It is lower than the score obtained on the D600 because of sharpness is identic and pixel noise is higher on Nikon D800.
So in lowlight condition, the D600 is maybe a better option with this lens.
The DxOMark team