Miles Hecker has posted interesting test results in his Canon EOS big guns image quality shootout:

As some of you know, I am a landscape photographer. I migrated to full frame digital SLR’s from medium format film. I used to shoot 6×4.5, 6×7 and 6×9 film with the end product being prints of 20″x30″ and larger. As such, I chose to investigate only one area of the 5Dmk2 in this exercise, overall image quality or IQ for short. For this test, I decided to construct a still life with a wide range of color, lots of detail and very controlled lighting to obtain what for me are valid results.The test would produce 100% crops for pixel peeping. The final analysis of IQ however would be made using real life obsevers and detailed sections of 16″x24″ and 20″x30″ photographic prints.

What I like about his test methodology is that it eliminates the very difficult issue of normalizing on-screen tests of cameras with different sensor sizes and photosite densities but doing something that I have felt would make the most sense, comparing large prints from the different test cameras. In this case he tested the Canon EOS 1DsM3, 5D2, 5D, and 50D. 

I won’t spoil the fun by telling you the results here, but let’s just say I’m not at all surprised at the results.