2018 15" MacBook Pro (RP555X) [8th,6C,H] + RX 580 @ 32Gbps-TB3 (Razer Core X) + macOS 10.15.1 [koncept_zero]  

System specs

MacBook Pro 15" Mid 2018 "MacBookPro15,1" (A1990)

2.6 GHz six-core Intel Core i7 Coffee Lake (8850H), up to 4.3 GHz

16 GB DDR4

AMD Radeon Pro 555X

Intel Iris Plus Graphics 630

MacOS Catalina 10.15.1

256 GB SSD

eGPU hardware

Razer Core X

AMD Sapphire Pulse  RX 580  8GB GDDR5

Apple TB3 cable to eGPU

Display port cable to Samsung UE590 28" 4k monitor

Installation steps

None. Natively supported.

Benchmarks

I bought this egpu purely for 4k video work in davinci resolve. I did perform some gaming benchmarks for fun.

Metal Internal 555x Geekbench - 13570 score

OpenCL Internal 555x Geekbench - 12959 score

Metal RX 580 Geekbench - 33468 score

OpenCL RX 580 Geekbench - 38635 score

Unigine Heaven RX580 - 1432 score, 56.9 avg fps, 1080p, Quality Ultra, Tessellation Disabled, Min fps 14.4, Max fps 94.3

Davinci Resolve 16 Export Benchmark: I exported A 1 minute 4k timeline using h.264 footage exporting to the youtube 4k preset. I did not use proxy files or render cache. All project files were living on the internal SSD. Fwiw, I performed all the tests with an external SSD and the times were nearly the same.

Using Metal and all available GPU's resulted in a 1:45 export time. 

Using only the external gpu with Metal took 1:57. 

Using only the internal 555x with Metal took 2:37.