A reader who purchased the new Vello BG-N19 battery grip for Nikon D850 sent me an email to inform me that he could not get 9 fps burst rate even with the bigger battery. With the Vello grip on the D850 7 fps is the best you can do.
Update – a reader sent me this picture of his Vello BG-N19 battery grip for Nikon D850 doing 9fps:
