The D810, Fast Action Handling?

As the title says. I can Google this title to death, but i'd rather have real world users give their opinions. Now, I love the D800, its a fantastic piece of work, but i found it a bit wanting in the fast action arena. I know it has some of the stuff like Expeed 4 from the D4S, but, before i do take the plunge, has anybody used one for fast, fast action, y'know, Motorsports, BIF, Aviation etc, and what are your thoughts??

Anyone with a D810 might know better but from what I read and (mis)understood:

D810 = slow & low
D750 = fast & high

Not saying they're bad at the other.