2017 27" iMac 5K (RP570) [7th,4C] + RX 5700 XT @ 32Gbps-TB3 (Razer Core X) + macOS 10.15.4 [Aiwi]  

System specs (model inc screen size, CPU, iGPU, dGPU, operating system)

• 2017 27" iMac 5K
• 3.4GHz Quad-Core i5 7500
• 32GB DDR4 2666MHz
• AMD 570 4GB dGPU
• macOS Catalina 10.15.4

eGPU hardware (eGPU enclosure, video card, any third-party TB3 cable, any custom mods)

• Razer Core X
• Provided 50cm TB3 Cable
• Internal monitor acceleration

Hardware pictures (note: require 5+ posts for "attach files" button to appear. Or can link from say http://imgur.com )

• I'll need some more posts for this
• Basically an iMac with a Razer Core X on the right side

Installation steps (what did you do to get it all going?)

• Idle at macOS desktop
• Plug in the eGPU
• Everything works!
• Set eGPU preference for chosen apps
  • Right-click on app
  • Choose Show Info
  • Choose Prefer External GPU
• All set!

Benchmarks (Include a CUDA-Z or AIDA64 bandwidth pic. Optional: Valley, 3dmark, noting if it's on internal/external LCD )

• CS:GO - Internal Screen

  • 1440p - Low Settings - FPS Benchmark Map

    • Radeon Pro 570 avg: 121.72 fps

    • Radeon 5700 XT avg: 61.24 fps

  • (How to configure CS:GO to use eGPU) https://egpu.io/forums/postid/74029/

• Divinity Original Sin 2 - Internal Screen

  • 1440p - Ultra Settings

    • Radeon Pro 570 avg: 45 fps

    • Radeon 5700 XT avg: 60 fps (capped despite v-sync and frame cap off)

  • 5K - Ultra Settings

    • Radeon Pro 570 avg: 14

    • Radeon 5700 XT avg: 35

Comments (eg: how has the eGPU improved your workflow or gaming)

• I'm not sure I think it's ideal to buy a Radeon 5700 XT for gaming in macOS on a 2017 5K iMac, in particular with internal monitor acceleration.
• My tests using an RTX 2070 in Windows 10 yielded better results. But the convenience of staying in macOS is hard to beat.
• In some games, like CS:GO, the eGPU rendered a huge performance loss at 1440p, Low settings.
• I would probably suggest setting up a gaming server and streaming from it instead, to be honest.
• Moonlight streaming or Parsec gives amazing performance from my decade-old Mac Pro with a Xeon X5690 and RTX 2070. This way my iMac runs cool and the heat is generated somewhere else in my house.
• The only problem with streaming is the iMac GPU's HVEC hardware decoder being limited to max 4K. (So, no 5K streaming) 🙁