I am not an engineer, so I would be curious if anyone knows: Does the slight drop in file size from the Mark II, 5D reflect a tradeoff that was necessary to improve results at higher ISOs? A second question: Although the ISO outer limit is higher on this camera than earlier ones, will this camera improve the results at the typical ISOs that we have been using: 800, 1600, 3200, or do those stay the same?
As an aside, I took a seminar from a very experienced professional two years ago--he has written a book on making your own darkroom chemicals, so he is a technically savvy user. He was screaming that 21 on the Mark II,5D was more than was necessary. He claimed that 18 was the maximum necessary for quality results. His comments are pretty interesting now.