Any chance you could make the RAW files available?
There is a slight but obvious focus difference between the shots. In the IQ shot, the red flower petals sticking forward turn soft. However, the amount of detail difference in the flower center is quite apparent, and the IQ shots seems to render a deeper colorsaturation curve and better separation of color. I wonder whether the latter is merely attributable to a different color profile, or whether it is a bitdepth issue.
Oddly enough, it looks as if the D800 reproduces better texture, but that may be due to the focus difference.