My experience, at this point, is limited, as I acquired my D500 in November 2017, and my D5 in February 2018, plus, some minor arm/shoulder injuries have limited my hand-held shooting, and I took delivery of a gimbal head only days ago. If “reach” is more important than performance at high ISO, I would think the D500 to be the better choice. If high ISO performance is more important, well, the D5 would seem to be the better choice. These factors are why I bought one of each. (A modest financial windfall enabled the recent purchase of a D5, for myself, and a D850, for my wife.)
This assumes we disregard the factors of frame rate, the D5’s integral vertical grip, and whatever differences may exist in the AF accuracy and acquisition. (I have yet to really test for differences in AF.)