GPU

Ritz

I was wondering whether I should wait for the
ASUS GeForce GTX 1660 Super TUF Overclocked Dual-Fan 6GB GDDR6 PCIe 3.0 Graphics Card
to come back in stock or if I should buy the 
ASUS Radeon RX 580 Dual Overclocked Dual-Fan 8GB GDDR5 PCIe 3.0 Graphics Card
right now. 
https://www.microcenter.com/site/content/custom-pc-builder-amd.aspx
Those are the pc parts I currently have.

JS_MC

I'd say that there is a noticeable difference between the two GPUs performance.

I found this video showing benchmarks of their performance.

I'd love to take a look at the rest of your build but the link you shared doesn't have your build. If you could share the link on the right of the page under the "Share" panel, I'd be happy to share more of my thoughts. 😁