I wonder how many of the people (usually with posts in the hundreds if that) who are going on about taking pictures and technique are or ever have been pro photographers, shoot anywhere near the shot count per week of pro photographers or in any case rely on their output to put bread on the table? When I read people throwing the phrase 'pixel peeping' at pro photographers it really makes my blood boil.
BTW Brainiac, I always found iso 200 an anomoly on my 5D's, a lot noisier than 100 and less DR or shadow detail than iso 400. No idea why. Ditto 800 compared to 1600 which again seems far better (1600 that is) unless 800 is exposed perfectly using ETTR. Could it be that like the 5D, certain iso's are 'fake' steps which are less able than certain higher iso's? I assume a 1 series would have better firmware enabling different iso's, my 1Ds didn't show this phenomenon, heck the 5D was the first non 1 series to have third stop iso's and we know that they cause more trouble than they are worth. Methinks try iso's 100/400 and see if you get better results.