So I found something interesting-and fun, metal acceleration on both a GTX770 and RX580 and hardware acceleration as well as I know to test it in both Mojave 10.14.3 and Win10-just no display in Mojave via the RX580. My NVIDIA GPU is a MVC flashed GTX 770 Founders Edition 2GB-and reports correctly as a 770 since I purchased in 2016 from eBay. Doubtful a MVC original-but the bios is locked reports as such; I got it from an east coast seller. Possible it was just re-sold to me though. I've been told the Quadro 4000 hangs on boot if attempting to boot Mojave with a Polaris: My AMD GPU is a Sapphire Pulse RX580 8GB standard dual bios OOTB, using the primary bios. I was very happy with this setup's overall perfomance in both macOS and Window but sorely missed Bootscreen and PhysX in Windows. Use caution-you can still trigger shutdowns if only using the PCIe boosters (i.e., DO NOT attempt from the Aux Boosters ALONE as any rendering will likely trigger a shutdown). Have a plan to provide power before even considering dual GPU's of any configuration long-term. After getting both a cards running self regulated with the GTX additional power via the Aux Boosters and a Powerlink, and the RX580 via a Pixlas mod. I had planned running the GTX 770 from the Pixlas mod, but found shutdowns were still triggered even under Bootcamp boot unless power limted in Afterburner in kernal mode. Returning the GTX 770 to the PCIe Aux Boosters and Powerlink, and routing direct power to the RX 580 from the PSU solder points fixed the need to limit the power and allows full rendering in both OS's. In my personal opinion-a single lane solution such the Quadro 4000 for Mac (Fermi but I am unsure of Metal capability) or flashed single lane Kepler would be far closer to the spec power envelope for a standard workstation application but this is what I have tested and worked in limited function. The RX580 in slot 1 was my first attempt, which worked-but with the same limitations I have currently, but the RX580 would run hotter due to Chill engaging (but not getting hot enough to trigger the fans). The 580 in slot 1 idles at 42 deg C, but in slot 2 it will idle at 38 deg C (prob cause the GTX FE's fan is circulating right next to the RX580's heatsink). Also, the GTX required a stand-off when in slot 2 to prevent the RX's fan's from clipping the solder-point's on my GTX which does not have a backplate. A secondary case and PSU could be warranted-but even without display in macOS, the RX580 is providing accelerated compute that is visible by both app and monitor which are the main reason most of us use them and is why I absolutely consider this a success. In macOS: 10.13.6 (17G4015- Baseline): 1) Both cards functional including NVIDIA web-drivers engaged, CUDA, and compute via the GTX. 2) Display via both the RX 580 and GTX 770 using both Apple and NVIDIA 3220.127.116.11.15.108 web-drivers; natively or using manufacturer's drivers when only one GPU is attempted to display at a time. 3) FCPX fully utilizes both cards for compute. RED 6K samples debayering adjustments behavior was acceptable to me-I don't deal with RED files regularly though. 4) Any attempt of dual GPU display output creates an immediate log-out of the OS (with either drivers engaged). 10.14.5: 5) GTX770 must be used as primary-DP is functional (but when swapped to RX580 is not). 6) CLing is reporting Metal acceleration in both GPU's 7) FCPX does not appear to use the RX580, but Compressor does as a booster GPU. 8) Heaven/Valley uses only the GTX770, but recognizes the RX580's presence (or I have just not been successful in engaging the RX580 yet). 9) I am hoping a second monitor may change #6/#7 (or future software updates?). 10) Attempts at dual GPU display output are recognized by the OS and are visible by the OS under the Display/Arrangement Tab, but the desktop rendered by the RX580 does not output. In Win10: 10) Best to use the RX580 as primary-both cards are usable. 10) GTX770 functions perfectly as a dedicated PhysX/CUDA card when using RX580's DP. 12) Certain settings on each AMD/NVIDIA control panel are only accessible when a monitor is connected to each manufacturer's card, so PhysX must be set to the GTX in the NVIDIA Control Panel prior to swapping to RX580 for use in Windows. It only needs to be done once usually, unless you move the cards slot location. 13) Ensure your cards are properly powered by getting a second PSU or provide power in an adequate manor. I have a mDP switch that I've re-purposed (previously was buggy at times when using w/ my MBP, so I don't recommend it by name brand), that's working well for now between GPU's. When setting up I was just swapping the DP cable by hand once booted to Windows between the GTX/RX where hot-swaps aren't a problem. They aren't a problem in macOS, but again-you just don't have a display via the RX580 in Mojave. I am planning a Pixlas mod to eventually power the RX580, or secondary PSU for both (undecided)-but wanted to share this setups viability for those that already have those bases covered. I personally favor a secondary PSU for longer-term use, but this is certainly viable for my use in Testing.