Whist I agree with you about the lag to what you SEE (clearly more with EVF) the lag to what you GET is much less without the mirror. The X-T1 especially seemed to give you exactly what you saw when you pressed the shutter - the A7s with the electronic shutter seemed pretty good as well. You see it later . . . but get it sooner (if you see what I mean).
Someone showed me a good real life test once - you sit in a cafe with the open door about ten feet away and try and catch people as they walk past the door - it's amazing the difference between one camera and another. . . . and how many of them just present you with a photo of an empty doorway!
I think Jorgen's real reason for the D810 is the inherently better tracking with an SLR - as you say - car racing.