I just stumbled across an interesting article that argues that the native ISOs for the 5D and 7D are not in multiples of 160 (ISO 160, 320, 520, etc) like a lot of people say, but instead multiples of 100 (ISO 100, 200, 300, etc) as you find on the Rebels and the rest of Canon’s lower level cameras.  It argues that the “cleaner” ISOs are cleaner because they are digitally pulled from the native ISOs which hides the noise more, but also looses some dynamic range.  The ISOs outside of the 100s and 160s multiples are then digitally pushed from the native ISOs, which is why they are a bit noisier than then other two.

It makes sense to me, but regardless if it’s true or not, it is an interesting read if you are interested in such things.

http://shootintheshot.joshsilfen.com/2010/05/13/canon-hd-dslr-native-iso/