2015 27" iMac 5K (R9 M390) [6th,4C] + RX 580 @ 16Gbps-TB2>TB3 (Razer Core X) + macOS 10.15.1 [Koncept_Zero] // for Davinci Resolve & tested 5700 XT  

System specs

27" iMac late 2015 17,1, (thunderbolt 2)

3.2 GHz Quad-Core Intel Core i5

32GB Ram

1 TB Fusion

AMD Radeon R9 M390 2GB

MacOS Catalina 10.15.1

eGPU hardware

Razer Core X

AMD Sapphire Pulse RX 580 8GB GDDR5

Apple TB3->TB2 adapter + OWC 0.5m TB2 -> TB2 cable

Display port cable to Samsung UE590 28" 4k monitor

Installation steps

Followed the steps outlined here: https://github.com/mayankk2308/purge-wrangler/blob/master/README.md

For disabling the SIP, I left out the "$" in the instructions linked above. This maybe code speak that I was to ignore regardless.

Benchmarks

I bought this egpu purely for 4k video worki n davinci resolve. This is really all I can benchmark. This is exporting a 1 minute h.264 4k file to 422 LT 4k without using optimized media or render cache and it took 1:54. The 5700 XT ran this test in 2:40. The internal GPU ran this is 4:44.

Here is the same test as above, but with using optimized media and render cache: 0:34. The internal GPU ran this same test in a staggering 0:36. The 5700 XT ran this test in 0:41.

For fun, here are some gaming benchmarks:

Comments

The benchmarks are what they are but this computer can now play diablo 3 on near top settings and still get decent FPS. This is the only computer game I own. This system was really put together for Davinci Resolve. I will say DR 16 is better optimized than 15 was. The same test yielded worse results until I upgraded to 16. Once there is render cache in davinci resolve, the timeline holds true at the timeline frame rate with 4k h.264 footage. I've only tried 23.976. The internal gpu could not play back the footage under any circumstance unless it was 1080p or less. Adobe Photoshop CC 2020 runs a little smoother. Certain tools don't lag now.

I also bought the XFX Radeon RX 5700 XT. In most tests, it performed worse except for the Unigine test. in Unigine, it blows the RX580 out of the water. But when I turned on Diablo 3, it was nearly as bad as the internal GPU! Also, the 5700 XT DOES NOT work with DR15! This GPU's drivers have a long way to go and I just can't justify the extra cost nor do I want to wait for it to be optimized. I'll be returning it.