2017 27" iMac 5K (RP570) [7th,4C] + RX 5700 XT @ 32Gbps-TB3 (Razer Core X) + macOS 10.15.7 & Win10 2004  

System spec:

• 2017 27" iMac 5K
• 3.6GHz Quad-Core i7 7700
• 48GB DDR4 2666MHz
• AMD RP 570 4GB dGPU
• macOS Catalina 10.15.7
• Windows 10 Pro 2004 build 19041.508

eGPU hardware:

• Gigabyte Radeon RX 5700 XT Gaming OC 8G
• Razer Core X
• Belkin Active 2m TB3 Cable
• External 4K 60Hz LG27UL650-W

Installation steps:

macOS 10.15.7

• Just plug and play after boot

Windows

1. Update to Windows 10 v2004
2. Install Adrenaline August 2020 Blue Enterprise Edition Driver from bootcampdrivers.com following their instructions (DDU in safe mode first then install after reboot)
3. Shut down
4. Connect TB 3 cable to iMac and power on eGPU (I'm using DP from eGPU to external monitor)
5. Power on iMac (I can only get eGPU working by cold booting in Windows and I set bootcamp as my default startup disk)
6. Enjoy!

Benchmarks:

• I am not able to get full performance on macOS, tried using dummy hdmi/DP but they don't seem to help (58,303 for Metal and 56,347 for Open CL on Geekbench 5)
• On Windows I am able to get the most out of it (70,405 for Open CL and 39,551 for Vulkan on Geekbench 5)
• Unigine Superposition Benchmark 1080p medium runs between 15-35fps depending on scenes
• Most games that I play run at 2K resolution 60fps High settings (eg. Forza Horizon 4, GTA V, Civilisation VI)
• MS Flight Sim runs at 2k resolution medium settings 30fps
• Export time for large photoshop files were improved slightly but this doesn't bother me much anyway

Comments:

• I was lucky that I didn't have to tinker much to get it working in bootcamp but I still can't figure out how to fully utilise the performance on macOS
• There was a problem with MS Flight Sim initially as the game refuse to run on eGPU, I tried disabling dGPU, selecting high performance GPU through system settings but they didn't work still. In the end I changed the display option to only display on my external monitor (yes, by disabling my 5k display) then the game runs perfectly. I was able to reenable my iMac display after loading up the game and use it as my second monitor.
• Noise level is bearable as I sit my eGPU under the desk and I use headphones while gaming/working
• Very happy with the performance on Windows but not so much on mac (hopefully Apple sort out their driver/whatever issue with eGPU soon)