I rented the R and didn't notice focus speed, but them again landscapes don't move all that much, and I didn't shoot birds with the R.
I shot a rugby tournament with a 5DsR on a 100-400II and never felt it was slow whatsoever. If (and this is the big if) I kept the focus point on a human, the shots were (I think) 100% accurate every time.
We're a Canon/Profoto family: five cameras, sixteen lenses, fifteen Profoto lights, too many modifiers.