iMac 5k late 2014 + Akitio Node + GTX 980Ti +external monitor
My previous set is iMac 5k late 2014 i7 4790K, 16G ram, 512G ssd, AMD M295X 4G, Bootcamp Win10, with an external gaming monitor AOC AG271QX 1440p 144hz for FPS and racing games. I use both MAC OS and Win10. Win10 is mostly for gaming.
My main motivation of adding the eGPU was that my iMac was quite slow and hot when running PUBG. Average 20-40 fps even with the lowest image quality settings @ 1080p, with frequent stutter issues. Lower the resolution to 720p makes it playable @ 60-70 fps but the image quality looks really bad, especially on the 27 inch display.
Node was connected to the iMac using a thunderbolt cable and an Apple tb 3 to tb 2 adaptor. And the external monitor was connected to the eGPU by HDMI cable (I saved the displayport on the monitor to connect it directly to the iMac when I don't want to activate the eGPU).
After all connected I installed the latest version Nvidia driver and Win10 can immediately recognise the GTX 980Ti. But when rebooting I got the ACPI BIOS error if the eGPU is connected. And if I let the system start without the eGPU and plug it in after entering Win10 the eGPU won't work.
After doing some research I found this Youtube video (credit to Kangwon Lee). The solution is to hot plug the eGPU in after choosing win10 from the boot option. It seems that the timing can be different for different machines. Mine just work when I plug it in right after seeing the Windows logo. After 2-3 times practice, now I can get the eGPU work everytime, and it does have some flexible room to work with.
Performance improvement is quite significant. PUBG now runs smoothly @1080p with 90-100+ fps on medium settings, and 70-90 fps on high settings (bottlenecked by thunderbolt 2). The game becomes far more enjoyable with no stutter issue at all; And although CS GO is a famous CPU intensive game, its performance is also improved from around 150-180 fps to 270-299 fps (game capped @ 300fps, I use 1920x1200 16:10 streched resolution, low settings, 2X AA).
Here are some more issues and findings:
1) When eGPU is powering the external monitor, the 5K display powered by the internal AMD M295X becomes a bit laggy. I can feel the lag when I watch a movie or type on the 5K display. The problem is gone if I lower the desktop resolution of the 5K display to 1440p. At 4K resolution the problem gets smaller but you can still feel it. It seems like an internal bandwidth issue. I have tried disconnect the eGPU and the M295X has no problem powering both the 5K display and the external monitor under both MAC OS and Win10 without any lag.
2) The GTX 980Ti cannot utilise the FreeSync function of my external monitor. I got it with the Node but may need to switch to an AMD card in the future if FreeSync is needed.
3) I thought the eGPU can make the temperature of the internal M295x lower. But it seems that the M295X is still very hot even though I put no window or program on the 5K display. And it's quite a surprise for me that its temperature is a lot higher than the GTX 980Ti.
4) I have tried different ports for my monitor. Displayport 1.2 and HDMI 2.0 can support 144hz @1440p. DVI-D can support 144hz @1080p. But when I use it @1440p it can only support 60hz.