System Definitions Revisited
All along, I've always preferred using using iMac18,x or iMac19,1 system definitions with IGPU enabled on this hack because of the similarities with CPU and motherboard chipset. I did test the iMacPro1,1 system definition way back when the iMac Pro was first released and, while it worked fine, I ended up going back to iMac18,x.
With the release of macOS 10.14.5, Apple made some changes to how macOS handles GPUs and they improved h.264 and HEVC encoding/decoding handling on iMac Pros. I decided to give the iMacPro1,1 system definition another try. Here's what I found.
View attachment 411331
As you can see, everything is working with iMacPro1,1. There are no compromises. It's only been about two days since I started retesting this system definition, but it has been running great. Until I encounter any issues, I'm going to be sticking with this.