When shooting in iTTL mode, Matrix is my standard and for slow shutter like 1/80 I normally use Rear Sync. There was nothing in the resulting images to suggest a problem and I would not have noticed the difference except this time, I was sharing the SB900 between two cameras and noticed the difference in consistency. I tried some test shots tonight with the D800 and same flash, with same settings and exposure frame to frame was closer but still not as consistent as the D7000. As I mentioned, flash is the only mode I have seen this, ambient light shot tonight and at the event were fine.
I extended the experiment tonight by getting 2 SB900's off cameras using fully manual and there was almost no difference in the 20 or so frames with the D800. There was no obvious difference when switching SB900's.
I tried a couple with ND filters and wide open 2.8, thinking there might be a slight case of sticking aperture but I could not tell anything for sure with only a few frames. I am starting to think the D800 is normal and the D7000 is just abnormally consistent;>)
I do not consider it a problem, just an observation, a curiosity more than a complaint. After using both for the last two events(I've taken the D7000 in the past but not brought it out when shooting the D800) I find that I really like that combination. Stan St Petersburg Russia