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


New Member
Joined: 5 years ago

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:

  Internal Display UHD External Display UHD
Horizon: Zero Dawn ~30 - 35 FPS on highest Settings, massive Framedrops ~45 - 60 FPS on highest Settings
The Witcher 3: Wild Hunt ~45 - 50 FPS on highest Settings, massive Framedrops ~60 - 75 FPS on highest Settings


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!

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

Eminent Member
Joined: 3 years ago

@sudelnuppe, you should be able to up the FPS in The Withcer 3 drastically by reducing "Foliage Visibility Distance" in the Graphics Options (has huge impact on the bandwidth).

Best regards



2019 15" Lenovo Yoga C940 (GTX1650) [9th,6C,H] + RTX 2070 Super @ 32Gbps-TB3 (Razer Core X Chroma) + Win10 [build link]  

Eminent Member
Joined: 2 years ago

did your 3090 came with a 3x8 pins? 

Razer 15 advanced model (2019) 32gb/1tbssd 2070 maxq w/ Razer core x chroma (3080 evga ftw3 ultra)

New Member
Joined: 5 years ago

@elel_penaflorida_mariano, No, it has a 2x8 configuration. It's a Palit RTX 3090 Gaming Pro PC


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

Mini i5
Prominent Member
Joined: 3 years ago


Nice build. Good to hear Windows 20H2 runs in Bootcamp without error 12 on your 2020 iMac. 😎


2018 Mac Mini [8th,6C,B] + RX 6600 XT @ 32Gbps-TB3 (Sonnet Breakaway 650) + macOS 12.1 & Win10 21H1 [build link]  

bereal liked
Trusted Member
Joined: 5 years ago

This is a pretty serious build! Have you ever test two eGPUs on your iMac? Or can it only handle a single eGPU?

Ryzen 9 3950x 16-core CPU
64GB RAM @ 2666 Mhz
RTX 2070 Super and GTX 1080 dGPUs

Active Member
Joined: 1 year ago

Nice build!

Do you have some Data in the overall Performance gain compared to your stock iMac


This post was modified 1 year ago

To do: Create my signature with system and expected eGPU configuration information to give context to my posts. I have no builds.