All the specs look pretty solid. Here's my thoughts -
AF:
Ok, Canon did not go for paper-specs and up the number of points. This shows that the 61 point system is more than capable. And the number of points isn't everything. But instead, the quality and speed of these points. Critics will bash Canon and say that Canon is recycling a 2011-era AF system in their flagship. However, the reality is this system is very strong and shows Canon was very far ahead of the competition.
I'm a little bit disappointed by the -3 EV autofocus, they should have pushed for -4 EV. I wonder if there are drawbacks to the AF system for going so very low light (speed or accuracy?) Time will tell.
Canon always suits their 1D for the needs of the pros who use and buy the 1D series. I doubt -4 EV was high up on the wants or needs list.
SENSOR:
No one knows anything until RAW image tests are done, so it's going to be a while. However, the ISO claims are well below that of Nikon.
The possibilities are:
Canon has only made a marginal leap in ISO.
Canon is more realistic with their ISO claims than Nikon.
Canon has made a big leap in ISO, changing the standards for IQ at high ISO's. In other words, 25,600 is now going to be cleaner than the 25,600 of previous generation WITHOUT having to add stops to the top end of the "native" ISO. This would imply that previous generation high ISO native limits were pushed too far with too weak of IQ. I would agree with this, as few people considered 25,600 to be useable. If the majority of users do not consider photographs from that setting to be usable, it shouldn't be in the "native" range. Just my opinion.
Canon is falling behind Nikon in ISO.
Canon has not improved ISO much, but instead relies more on noise reduction processing. This is what I suspect Nikon has done a lot of.
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Other thoughts-
The camera looks solid. Would have been nice to see a 1/300 sync speed, but that's not a biggie. I doubt many 1DX owners will upgrade unless they absolutely need 4K or the F8 AF improvements.
This is going to be a big upgrade for all the other 1D series owners. There are many, many out there still cranking away with the older flagships.
Versus Nikon -
Canon has gone more for improving the existing pro features and things that sports shooters really need. Whereas Nikon is still in catch-up mode on that. The 1DX2 will still be the sports and action king. I don't want to prejudge as I'm sure IQ has improved, but it is likely Canon has made an incremental improvement, not a big improvement in IQ.
However, there's a segment of users out there who are NOT sports and action shooters. They are general photographers or even wedding pros who use flagships. For them, high ISO, low light and IQ will matter more than it does for the straight up sports shooters.
The IQ results will matter more to these types. Although, the Canon glass system is better and most are invested - I don't expect many defections if there's a big difference. First time users making the leap to flagship camera might switch if they have the need for that kind of ISO and DR.
Time will tell what the IQ results will be.
I think it will be a combination of - Nikon overhyping their IQ and sensor, and Canon making small, incremental improvements and being more honest about their specs. With Nikon probably edging Canon out in sensor IQ only by a small amount. With Canon glass making up a big part of the difference. Leaving Nikon only the DR advantage.