I have had the 7D2 for about 18months and rented the 1Dx2 a couple of weeks ago. Although I still need to finish reviewing the files I think the reach advantage in good light is not huge in my opinion (I can post a couple of images a bit later today). In fact it is so close I would look at other reasons for changing bodies.
With birds in flight, the wider view of the 1Dx2 (or any FF camera) makes it easier to track if the focus point moves off the subject. But because the subject is smaller in the VF it can make it harder to keep the focus point in precisely the right place (for example the eye).
The reason I was really interested in the 1Dx2 was performance at ISO 1600 and above, and it seems the 1Dx2 does have some advantages (or more exactly, is no worse) even when cropped to the same FOV as the 7D2. Again, examples to follow.
But the AF....that is a different matter. The 1Dx2 is far more assured and I can feel the difference in how is snaps the lens into focus. And it is better at tracking moving subjects especially in lower light levels.
For me, the choice is wider aperture lens or the 1Dx2. Wider aperture or better ISO performance. And a damned difficult choice it is.
If the refinements of 1Dx2 over 1Dx are not high priority, and if image quality is the main driver then seriously consider the 1Dx over the Mkii.