On the crops below you can see how the 50D images get softer as you increase ISO and noise reduction becomes more aggressive. You can preserve more detail by switching noise reduction off but, as you would expect, you'll pay for the extra detail with some extra noise. Despite the noise reduction set to 'Standard' you can also see chroma noise creeping in pretty early on. While ISO6400 might be usable for small size low-res prints ISO 12800 is firmly based in the emergency camp.
ISO 800
Canon EOS 50D
Nikon D300
Sony DSLR-A700
Pentax K20D
Canon EOS 40D
ISO 1600
Canon EOS 50D
Nikon D300
Sony DSLR-A700
Pentax K20D
Canon EOS 40D
ISO 3200
Canon EOS 50D
Nikon D300
Sony DSLR-A700
Pentax K20D
Canon EOS 40D (Equiv*)
ISO 6400
Canon EOS 50D (Equiv*)
Nikon D300 (Equiv*)
Sony DSLR-A700
Pentax K20D (Equiv*)
ISO 12800
Canon EOS 50D(Equiv*)
* Additional sensitivity settings denoted by the manufacturer as boosted or equivalent to that ISO setting.
