I'll have a lot, lot more tests tomorrow, but so far I haven't seen any difference in IQ at all, around ISO 100-400. I didn't crop either, so I have a lot more to examine. As can be expected, the color rendition is slightly different, as for my tests I'll just leave each cam in Portrait Mode (my favorite on the 1Ds 3). The tests I'll be doing will be among the 1D X, 1D Mark IV, and 5D Mark III. I think those are very appropriate comparisons regarding the magnitude of each camera.