East Wind Photography, regarding your issue with the shutter noise of the 1DX. I can certainly understand wanting it quieter. However, if that were the only issue, couldn't you simply try one of the noise reducing guards or wraps that are available? (I know it wasn't the only issue, of course...and obviously having to use a noise guard of some kind, would be more of a hassle than not using one.)
Given your choice of shooting in decent light, and your lack of a real need for anything faster than 6fps, I can certainly see why you would opt for a 5D3 over the 1DX, especially given the price difference. Which kind of gets me back to...why would you even try a 1DX at all?
It seems to me, that buying a 1DX and not using it for its intended purposes, makes about as much sense as buying a sports car, as many of the doctors and lawyers do...but only getting black or silver paint, and never going over the speed limit. They want to show that they have a car that others would envy, but they won't use it for its intended purpose, and they choose an understated color to blend into the crowd...because otherwise their hospitals and law firms would think they were trying to stray from their wives.
I could be reading a bit too much into this, and the analogy isn't all that good I guess...sorry!
Pictured here is a small bird I shot the other day center-cropped out of the original 4752 pixel width, down to 1812 pixels, and then reduced to 1050 pixels in width (I admit the reduction down to 1050 is obviously helping it). But still, this is basically only 38% of the full field of view of the original image. Shot through a window pane, handheld at only 1/320 sec, FF equivalent 320mm, with my lowly 5 year old crop camera, and my 70-200 f/4, at f/4 and 200mm. ISO 1600 (higher than your self-limited ISO 1000 on your much better, newer, bigger, more expensive, more masculine camera and lenses). The little bird was very cold in the wind, so I guess they puff out to stay warm. I would too! Instead I chose to stay in the warm and shoot through glass...and attempt to deal with rather terrible image softness.
(My poor attempt at trying to sharpen notwithstanding), I'm sure the grain itself is far below your taste, but it's only barely worse than the limit of my taste. (Yes I went through 3 total stages of NR, first in ACR, then at full size in PS, then again at reduced size in PS...!). Obviously the composition itself isn't worthy of anyone wanting to display it. I have other wildlife shots that I feel, are worthy (not many are birds). I just don't have my own website yet, or enough knowledge about how to go about marketing them. At some point I'll figure it out.
My point though, is that I could get the same amount of grain at ISO 12,800, if not higher, on a 1DX. Quite possibly even ISO 16,000...So down at ISO 1000 with 1DX or 5D3, that's really like going 20mph on the interstate, in that gull gray Ferrari 458 Italia...