All the images from the D700 are 4,256 pixels x 2,832 pixels on a 36.0mm x 23.9mm sensor. The D800 has an image measuring 7,360 pixels x 4,912 pixels on a sensor 35.9mm x 24mm. Both are FX sensors so there is no crop factor as there would be on DX. The DX crop on the D800 is to the DX sensor size - 4,800 pixels x 3,200 pixels.
The framing of the image through the lens on a D700 is the same as the D800, so to get a smaller crop of an image using a D700 you need to move closer or change lenses.
If you want to look at the performance of individual pixels, essentially you are wanting to look at something smaller than a DX crop on the D800.