I own 2 x 5D3's and have shot 4000 frames so far in low light situations and the 1Dx is at least equal or greater than two stops better than the 5D3. 12800 is better than 3200.Do you mean the 5d2? The 1dx isn't 2 stops better than the 5d3.
I'm not going to argue about it either. I edit an average 200 images a day. The 1Dx is everything Canon and others have said it is.
Yes it is. Remember, Canon upped the MP on the 5D3 whilst keeping the MP at relatively lower 18 on the 1Dx. Physics plays a bit part here. You've got considerably larger pixels and better developed tech in the 1Dx sensor. Also note this replaces two lines of 1D body. It's going to be good.
I still shoot portraits with 2004 tech in the 22mp medium format backs. Why? 9 micron pixels. Nice big fat light gathering pixels. This is why Canon hasn't gone crazy with the MP, there are limits. Same as why the D800 falls apart above ISO1600.... small pixels crammed onto a small sensor.
The same sort of rules apply to lenses and why they will always be a certain size. For me personally I would prefer a 1Dx with 12mp and clean ISO throughout but that's not going to happen