Just a thought.
Almost all of my work is weddings and when choosing what lenses to use I nearly always go for the fastest I can, be they primes or zooms.
With the 1Dx being so much better in ISO performance the 1 stop speed advantage of a 24-70 doesn't 'seem' to warrant using it when you compare it to a 24-105.
With the extra reach, IS, reduced weight in it's favour is it something you've considered yet?
For me the plane of focus on the 2.8 is nice but a lot of the time impractical when shooting a couple at an angle when F4 would be more suited.