I'm still using MacPro's 5.1 - and I've made an extra cable for power distribution from the SATA ports to the GPU-area for added power capabilities running the later GPU's from Nvidia. However, due to Mojave's lack of Nvidia drivers, I've acquired a pair of cheap second hand Radeon 580RX to test double 8-pin power consumption and Mojave on 5.1 workstations. They seem to process 6k Raw-files at almost real-time speed, but they don't seem to be able to both process and read at the same time in RedCine it seems. It buffers a segment in what seems like realtime, and then plays it back, etc., etc. It also stutters in DaVinci Resolve. Should they be linked with any kind of cable to work better in tandem on a Mac?