>>3598026>with the z 6 you'd get a much more reliable af, and a better iso perfomance.Can't speak to AF because I haven't handled those two. But the ISO performance is virtually identical. The D750 is more saturated in the dpreview test, which is probably a setting and not the sensor, but the noise pattern is as close as I've ever seen two cameras at all ISOs tested.
D850 is a good recommendation if you can stretch your budget.