''I put together a few quick frames from ISO 1600 to ISO 25600 for the Nikon D700 and Canon 5D Mark II tonight.  Nothing scientific, just a few shots snapped off at my desk.
Settings: tripod, aperture priority @ f/8, evaluative metering, auto white balance, ISO 1600-25600 in full stops - lenses used were 50mm f/1.8 on the Nikon & 50mm f/1.4 on the Canon - RAW capture - exported to JPEG via Lightroom with no edits other than the 100% crops
As you’ll see, the 5D Mark II tended to underexpose a bit, which I left alone for the purposes of this quick test. I’ll go more in-depth in a later post on these two cameras.
Click on any image to enlarge to full size (Note that I mildly resized the 100% crops to fit into the post, so you’ll need to click to get the 100% crop, which are between 650-800px wide for both cameras)  Also, bear in mind that the 5D Mark II full image files go up to 32MB+ in file size, so dial-up readers need not apply.'' Read the whole test here. You can buy the Canon 5D mk II here and Nikon D700 here.