Compared to...

Studio scene comparison (higher sensitivities - JPEG)

We've seen how the 1D Mark IV performs at high ISOs with various noise reduction settings but how does that compare to its peers? All images here are JPEG files, taken at standard settings with default noise reduction enabled. It should go without saying that careful post-processing of the equivalent raw files will yield more attractive results, albeit without the immediacy of shooting JPEG.

ISO 3200
ISO 6400
ISO 12,800
ISO 25,600
ISO 51,200
ISO 102,400
Canon EOS-1D Mark IV
Nikon D3S
Canon EOS 7D
Canon EOS-1D Mark III

We've seen that the 1D Mark IV is very competent up to ISO 6400 but struggles increasingly beyond that point. The D3S outdoes this by at least one stop in terms of both detail and saturation retention. The 7D trails the Mark IV by a small amount but the difference isn't huge (raising the question of why Canon feels the Mark IV should be allowed to continue up to ISO 102,400 when the 7D is limited three whole stops lower than that).

Bearing in mind that the Mark IV's APS-H sensor is 56% larger than the 7D's but 40% smaller than the D3S', it's surprising that the differences in noise and detail levels aren't greater. Even so, the differences are there and for any kind of shooting that demands immediate delivery of images (and hence the use of JPEGs), the Nikon remains the low-light king. There are examples of ISO 12,800 sports images in the samples gallery (taken alongside similar images from the D3S), to show the sorts of results that are possible and would have been unthinkable even as recently as three years ago.