Hi, I know this is slightly off-topic.
Wanted to share with you my MacBook Pro 4,1 (early 2008 model) running High Sierra and eGPU via the ExpressCard/34 port using the EXP GDC adapter (total $50 !). I run a Nvidia Geforce 560Ti (Fermi-based) card I had lying around, with 2GB of graphics memory, on the port (using Nvidia's latest Web drivers, not required though), which is connected through PCIe 1x speed effectively. Getting quite good performance, and up to 10 times faster than the original Geforce 8600m built into the machine.
As it really is connected directly onto the internal PCIe bus (as opposed to Thunderbolt eGPU) no software modifications or hacks are needed, it just works.
Thanks to DosDude for making it possible to run High Sierra on this beloved machine! Outstanding work!
Enjoy!