Joel:

I agree with Brant - not all pixels are created equal. I had read AlanF's bit on CR a while back and it seemed to agree with what I had found with the 1DX vs 7D. That is, although I was loosing reach (so to speak), I could heavily crop the 1DX and still come out with a better image. The 7D was not very friendly to cropping at all. Not to mention, I could raise the 1DX ISO up past the 7D's capability and still crop to get a better image. I would say the 7D-II has better pixels than the original 7D, so it is getting to be a tighter comparison. However, I would not discount that you are effectively magnifying the noise artifacts, and a better set of pixels with less noise is going to hold up to cropping better. If you want that sharp glassy look in the eye of the bird, it is much more difficult to achieve if it is speckled with noise. Good noise reduction procedures like you use are helpful, but they would be even more effective if you start with cleaner set of pixel data.

The rub is, the FF has to loose a lot of pixels to get to the same framing, but with the 1DX vs. 7D, I still found the 1DX's better file to create something more pleasing. I still have the 7D and pick it up occasionally to give my 400mm more "reach", but it does not take long to put it back down and put the lens on the 1DX.

I also noticed you go back and forth with your 1DX and 1D IV. Unfortunately for the IV, on a cloudy day with limited light, for the extra "reach" of 1.3X you need to increase the ISO(compared to the 1DX) to get a higher shutter speed to counter the shake issues with the higher effective Focal length. Now you have more noise compared to the 1DX which can shoot at a lower ISO because the effecting focal length has less shake issues. So now I have a cleaner file that I crop and compare to a noisier file - I would be curious to see which one produces a better picture... I would thing the 1DX, but it may be close.

Pat