2017 21" iMac 4K (RP560) [7th,4C,K] + RX Vega 56 @ 32Gbps-TB3 (Sonnet Breakaway 550) + macOS 10.14 & Win10 [semohe] // on external ssd  

System specs 
iMac (Retina 4K, 21.5-inch, 2017)
Processor 3,4 ghz intel core i5
ram 8gb
dGpu Radeon Pro 560 4gb
Mojave

eGPU hardware 
Sonnet Breakaway 550
AMD Radeon RX Vega 56 8gb
standard TB3 cable

Hardware pictures

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

For Mac Os Mojave is just plug and play, you can use it with internal or external monitor or both just great
For window 10, i spent 1 week to finally make it work. the problem is with the error 12. and after following Mikael's guide the error 12 is gone. it works with external ssd windows 10  boot. for now i can only use external monitor for windows 10. 

Benchmarks 
internal monitor on mac

external monitor on windows 10

thx eGPU.io

semohe