I vote 1950X for the benefits of the x399 platform.
Another thing to consider is the cooling for TR4. If you are reusing something for this build, keep in mind the baseplate of most heatsinks or waterblocks aren't large enough to cover the socket or don't have mounts, so you may need to factor...
For Sale:
Asus GTX 1080 8Gb- SOLD
Model: TURBO-GTX1080-8G
Specs: https://www.asus.com/us/Graphics-Cards/TURBO-GTX1080-8G/specifications/
Original box
Shipping to conus, prefer PayPal payment. Open to offers.