Upload & Sell: On
- slightly better viewfinder
That is debatable, as it suffers from the by now infamous "invisible AF point" problem. I definitely found the 1Ds3 viewfinder to be superior to the new one, by miles.
Oh, and just an FYI... if for some reason you do want the flashing red AF points in your 1Dx, just set "VF display illumination" to "ON"
Believe it or not, I have that turned on. But that works only in Servo mode, then you have the grid and ALL the AF points flashing, and it's a big circus altogether. All other cameras that I've had, starting with the 1N in the 90s, had the AF points illuminated in a sensible fashion so that they were always visible, whether it was at night or in the bright CA sun. Heck even my new SL1 does it right... and it's not nearly as offensive as you make it sound to be.
I have no idea why they had to "fix" something that wasn't broken for the past 20 years. The Nikon D4 gets it right, despite having an otherwise equally "nifty" viewfinder with superimposed grid and such.