2020 27" iMac (RP5500XT) [10th,10C] + RTX 3090 @ 32Gbps-TB3 (Razer Core X) + Win10 20H2  

System specs :

2020 iMac 27" - i9-10910/RP 5500xt/40GB RAM/512GB SSD

2x 4K UHD Displays

eGPU hardware :

RTX 3090 + Razer Core X + included 0.5m Thunderbolt 3 Cable

Installation steps :

Installation was pretty straightforward compared to an AMD GPU:

1. Install Bootcamp and all included drivers

2. Hot-Plug eGPU and install newest drivers

To get both the eGPU and dGPU up and running there is an optional third step:

(3.) Hot-Plug the eGPU after Windows has booted

Though this results in some issues with Bluetooth.

Furthermore Cold-Plug only seems to work with this extra step:

(3.) Set BootCamp as Startup-Disk in macOS

Benchmarks :

I currently tested only 2 Games:

Both games seem to be heavily starved by bandwidth. Especially HZD where it made almost no difference in performance when I switched from 4K to 1440p.

Comments :

Here I want to share same lessons I learned while trying this build:

1. Though the eGPU and dGPU can run at the same time, sometimes when trying to watch a YouTube video on the internal display either causes it to reload and use the dGPU or simply crash the whole System
2. I had to take off the shroud of the Razer Core which resulted in a temperature drop of ~12 degrees and a reduction in fan noise. The heat this card generates is insane, even when undervolted.
3. Gaming on the internal display seems to be hopeless. Though the frame rate at lower resolutions (1440p) is higher, you get annoying frame drops every few seconds.
4. Trying to Cold-Plug without setting BootCamp as the Startup-Disk just results in a Blackscreen when booting.
5. Sometimes Bluetooth just doesn't work. Probably an issue with resource allocation.

If you have any questions or Benchmark requests, let me know!