Hi Kim,
I'm probably one of the only geezers still shooting a pair of D850s, but I'm stubborn and cheap, so am sticking by my guns for the moment. To answer your question, so much depends upon the circumstances of course, but generally for BIF I shoot Manual with shutter speeds of 1/2500 or 1/3200, group AF, auto ISO, Continuous High (CH) shooting mode. AfOn button has been programmed to back button AF (BBAF). Naturally, if I'm looking to show wing motion or express subject speed, I'll slow the shutter speed down a lot, but to freeze action I Iike using a faster shutter that other folks might choose. Not sure if this is what you're looking for- please advise if not.