Your latest tests with your d4 and d800 with the bookcase incandescent and the driveway mixed sunlight and skylight show that your d4 and d800 are reasonably close in reproducing the actual scene-illumination color temp. As I mentioned earlier in this thread, these slight differences should be expected among different cam bodies of the same nikon model, as well as between cam bodies of different nikon models. However, the differences your manual presets are showing between the d4 and d800 with the bookcase under incandescent lighting are clearly greater than should be expected. Most likely due to the minor difficulties involved in properly doing a white-card or grey-card manual preset. Remember that the white or gray card need to be placed within the lighting that is incident on the scene. Just zoom into the reference card, keeping camera position the same, and make the manual presets with both cam bodies using the same lens. I always do my white/grey card reference shots in manual exposure mode, and zero-out the exposure on the cam body meter before pressing the shutter and setting the white balance. The easy thing to remember, whenever using multiple cam bodies, on location or in the studio, is that since the white balance is always slightly different between cam bodies, just set your cam bodies manually to the same white balance option in both cam bodies WB menu. Of course you will need to fine tune your white balance later between different cam body images in post-processing. But do not use any auto-white balance settings, as they will exaggerate the differences among and between the cam bodies.. Select an actual color temperature for your on-location scene and set the same temp for all your cam bodies. On-location, I always use a lot of strobe mixed with skylight, sand reflection, water reflection and whatever else I throw in, so I always set the different rental nikon bodies to the cam body manual white balance setting for flash, which is 5400 degrees kelvin, which is an option available on the d4 and d800 and d3x and every other nikon body I have ever worked with. Of course there are always slight differences between cam bodies regarding color temp, but they can all easily be smoothed out later with whatever image processing software you may be using. And if you are not using flash as your main illumination source, just set all cam bodies to the same white/grey card manual preset and you can correct the expected differences later in post-processing. Thanks for all your white-balance testing and thanks for taking the time to post your efforts, all your work can only help make all of us better nikon shooters. good luck.