Here is some perspective on why you want a DX for sports/wildlife.
If you want a 300mm 2.8 for an FX body you will need to get the Nikkor 300mm f2.8 ED VR II lens @ $5,500
To get 300mm 2.8 on a DX body you can just get the (Amazing) NIKKOR 70-200mm f/2.8 VR S @ $2,500 (200mm x 1.5 crop factor = 300mm)
The D500 has the same Multi-CAM 20K autofocus sensor module that's used in Nikon's flagship D5 ($6,500 camera).
Don't take my word for it.. Check out what people use on 'thephotoforum' and 'dpreview'