How I would describe 1dc video quality

[Asmundma]

For 4k you only have to use the A7R2 - with a very light prime or e.g. the cine FE 28-135 (200 in S35 mode) for video. Video is excellent, stills are EXELLENT (also with the FE28-135).  With native lenses, better autofocus  (e.g. eye focus tracking) or even with 5D3 (autofocus is way better on A7R2 then A7s).  Only for long takes > 30min in 4k you may need a recorder, also to eliminate the 30 minute limit + possible overheating. 

I see myself now selling off many Canon lenses, plan to keep the 1Dx for "extreme" sports with the longer primes (400) and the 70-200, maybe keep the 24-70 as well. for all normal focal length + wide - use the Sony. Have now used the A7R2 for 3-4 weeks I clearly see the the much better sensor (dynamic range and ability to push shadows) then current Canons. 

That said, everyone finds what works best for them, different priorities etc.