Comparison of 5D to 1D Mk II. All tests at ISO 3200, neutral picture style, zero sharpening, converted in DPP to JPG and combined in Photoshop Elements 3. Lens was the 70-200 f/2.8 zoom, tripod mounted, and zoomed to frame equally (I believe that this better simulates actual use, since we tend to select the lens that fits our position most often, or at least I do).

The first image shows 100% crops of the upper righthand corner of each image. Noise is similar.

The second image, the 5D image was reduced to approximately the same dimensions as the 1D Mk II, and then 100% crops were again compared. Note that the 5D noise is of a finer grain compared to the 1D Mk II when the shots are equalized in dimension.

The third image shows noise reduction from Photoshop Elements 3 applied to the second image. Note how the finer grain of the 5D results in a much cleaner, more detailed image in comparison.

Shot 4 is a small version of the entire scene as framed and shot.

Shot 5 is a 1000X1500 pixel version of the 1D Mk II shot at ISO 3200, with Photoshop Elements Noise Reduction applied.

Shot 6 is a 1000X 1500 pixel version of the 5D shot at ISO 3200, with Photoshop Elements Noise reduction applied in an equal amount to the 1D Mk II image.