There are quite a few good, somewhat older comparisons between the Canon 5D and the Nikon D3 and D700 in term sof per-pixel resolution, acutance, and noise. Garbz's conttntions about noise are very full of mathematicall blowhard numbers and incorrect assumptions, like his disagreement that noise is noise. The actual facts will tell you that there is chroma noise and luminance noise, and one looks like crap, and the other looks like film grain. Garbz seems to have the mind of a college student who studies physics, but lacks eyes and actual experience in photography to trust his own senses; noise "measurements" are very subjective,and quite often cameras with lower mathematical noise measurements look WORSE than cameras that turn in higher noise numbers on test charts. That is why noise "numbers" are not the same as actual images in terms of judging noise in terms of how the images actually "look".
Shocking as it might be, the Nikon D3 camera out in 2007, with the D700 following not too many months behind, at seven months after. The EOS 5D has a 12.8 megapixel sensor, the D3 and D700 have slightly smaller sensors with 12.1 or so effective megapixels. Anybody who wishes can do a Google search on noise comparisons between EOS 5D and Nikon D3 and D700,and will eventually find some real-world comparisons. Some of them were done on dPreview by a couple of well-known commercial studio photographers who were interested in the best FF d-slr performance. I downloaded the sample images back in 2007 and early 2008,and my own EYES showed me that the "old" Canon 5D delivered a slightly higher-resolution, higher-acutance picture than either the Nikon D3 or the D700. Very simple really--I looked at actual images, not noise graphs. It's a testament to Canon's sensor design, microlens design, and internal software that it took Nikon almost three years to come up with a FF sensor that ALMOST equalled the 5D's overall,total imaging capabilities in the 200-1600 range.
Visually, that the "old" EOS 5D is the equal,or better, of the Nikon D3 and D700 in terms of per-pixel sharpness, which is a combination of resolution and acutance, as well as noise, from ISO 200-1600. It is also very clear, according to the URL I linked to above that at EQUAL IMAGE SIZES, the new 7D loses out in terms of noise,and shows lower detail than the "old" Canon 5D. Both Canon and Nikon have figured out a 12-12.8MP FF sensor is sweet!
I love how a Norwegian Nikon lover challenges me, and how a newbie who has been involved in photography for less than a year challenges me, one no doubt thinking I am a Canon lover basking Nikon, the other thinking I am bashing on the two brand new 7D's he bought,and eager to try and convince me what I have seen with my own eyes is invalid. Funny...I own both systems. I like both, for different things. Everybody sees bias where none exists. Nikon fans and Canon fans see bias where none exists.
Check out MAJOR Nikon fanboy Ken Rockwell's comments here
Nikon D3 and D700 vs Canon 5D
"The Canon 5D excels in image quality. It's also the lightest and least expensive of these cameras. It has the sharpest pictures of these three cameras by a slight margin. If you're backpacking or shooting careful landscapes, the 5D could give superior image quality above anything from Nikon, at a bargain price. If you want the best picture quality for landscapes and huge enlargements, the 5D is the best camera. I'm not kidding: I have 20x30" (50 x 75cm) prints here, and the 5D is clearly superior. (Then again, medium format film is superior to any of these in 20x30" prints.)"
Wow,in actual tests of the three, the 5D proves to be the better imager!
Nikon D3, D300 and Canon 5D Sharpness Comparison
Canon 1Ds Mk III vs. Canon 5D vs. Nikon D3
Nikon D3X Sharpness Comparison
One of the most interesting tests was comparing 20x30 inch prints from the D3 and 5D and Nikon D40 here:
20x30" Print Comparison
Where the conclusion about PRINTED versus on-screen comparisons was made,
"I didn't expect such an obvious difference, but if you're too close, the Canon 5D is clearly superior to the D3. I shot the world's best 14-24mm on the D3, and Canon's not-as good (in the lab) 16-35mm L II on the 5D, and the 5D shot still smokes the D3 in sharpness. I shot the D3 on a tripod, and shot the 5D freehand. Both files were the same size.The 5D image is much better, but does show some lateral color fringes which the D3 corrects itself. If I had used the NEF from the D3 (shot but not shared here), many raw converters don't remove the fringes as does the D3 in its own JPGs.The on-print results are more striking than the differences seen on-screen at my sharpness comparison." Wow, yet another real comparison,and the "old" 5D makes a betetr 2030 inch print.
Combine Ken's multiple tests over several years, plus the tests of Fredric Frauhaus,and other commercial photographers, and it's pretty clear that Canon's original 5D sensor and image processor was *far* ahead of its time.
It's not just pixel count that determines how a camera performs, but how the images turn out. One of the more striking comments was from Rob Galbraith about why he prefers the 10.1 MP Canon 1D Mark III over the 12.1 MP Nikon D3: per-pixel image quality of the 1D Mark III is higher than that of the D3.
Last reference. Go here
Nikon D3 Review: 18. Photographic tests: Digital Photography Review
and use your own eyes to see which camera has more detail at ISO settings from 200 to 1600. The winner? Canon 5D, by a nose.