First elephant in the room: High Sierra is incredibly unstable. The devastation is only comparable to the first release of Lion’s public beta. Make sure all of your backup is up-and-running, preferably try it out on non-workstation. Kernel panic is a joke in this release. Perhaps ride it out till 3rd or 4th public beta. Currently Apple only supports (or enabled) specific GPUs for eGPU purposes. It has drivers, but you would not be able use it.
Second elephant in the room: GPU market is high; It’s out of control. At the time of purchase, I’ve read and received mixed reviews and suggestions on the “right” price. The reality is, the market is so heated to a point where if you stick to Apple’ choice of GPUs, you would pay triple of its original price from April. My suggestion is to ride it out. Wait until High Sierra hits at least GM, and then upgrade from whatever graphic card you were currently using with eGPU now.
Third elephant in the room: scripts and hack development for eGPU are slow and most of them dead. Mac’s eGPU community relies on one script, called automate-eGPU.sh by goalque. However, the development is ceased as of April 2017. Now with the coming High Sierra, we need a new hack; otherwise, you would be forced to choose from Radeon RX 470/480/570/580, all of which are also popular graphic cards for cryptocurrency mining purposes.
Fourth elephant in the room: while eGPU setup worked, manufacturer of both graphic cards and Thunderbolt enclosure do not officially support Mac as of late. In order to maintain your Thunderbolt devices, you may need to use Bootcamp, as not even virtual machine is prepared for Thunderbolt support. Again, we can only assume, with all the attention eGPU is getting, these official support will come within couple of years.
The setup is rather simple. I’ve hooked up Atikio Node to a Mac Mini (late 2014) via Thunderbolt 2. Provided you have an adaptor from Apple, –from Thunderbolt 3 to Thunderbolt 2– your Mac can communicate with Thunderbolt 3 devices. Any other Thunderbolt adaptor may not work, so don’t hesitate to invest in an adaptor. Then you simply follow instructions as to how to install automate-eGPU. Voila, your Mac is set to go and you can connect an external monitor through the graphic card.
What got me interested were two things: how much performance can I expect out of Thunderbolt 2 devices and is it possible to use all ATI cards on High Sierra? As for the first question, the benchmark showed about 10-20% of performance loss, with average of 15%. I expect the number to be quite lower on Thunderbolt 3, regardless of the fact that it can’t be 0. So if you have a Thunderbolt 2 enabled computer, eGPU may be an option for you.
As for the High Sierra, the answer is a brute no. So far I haven’t seen any hacks or scripts that enable graphic cards aside from that 4 selections. Any information from eGPU.io on the topic of freely choosing graphic cards seemed grim. It may be doable, but it may not be immediately available. My game plan at this stage would be: equip yourself with all the necessary gears but with a lesser graphic card, and buy supported the graphic card after High Sierra is announced. Optimally, Apple would add more GPUs to its selection of eGPUs.
updated Nov 24, 2017: new review with official version of High Sierra is now available.