You don't need to focus on a GPU for photo editing, what you really need to focus on is RAM, CPU, and Monitor.
https://pcpartpicker.com/list/XsR3tp
Check out the link above to see a custom build list.
-- What I chose and why --
CPU: 9700K will give you best core clock frequencies (amount of tasks per core) which photoshop prefers over multi-threaded perforamnce. So AMD performs worse on photoshop.
RAM: Anyhting above 3200MHz is ideal for optimal perfomance. Trident Z being the best ram on the market right now. And you have the money to spare apparently for the best.
Monitor: You can choose any other monitor you prefer but I highly recommend a monitor that has these qualities:
- IPS PANEL (For best colors)
- Anything...