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Damn... I think I'll wait for the (hopefully) 2019 Mac Pro.

Thanks for the info.
Start searching for a PC AMD HD 7950/HD 7970/R9-280 or NVIDIA GT680, both cards can be flashed with the Mac EFI and work nicely with Mojave.

GTX 680 is a 5' job with Windows, read Step-by-Step Instructions for Flashing GTX680.

Search locally, you probably will find a PC user selling one on the cheap, eBay people usually know that Mac users need this GPUs and they want to make big bucks selling this cards.

Both cards are faster than your current RX-560.
 
Thanks for the info. Thing is I bought this 560 last summer for a single video game and I'm not going to spend more cash on it. I placed the 120GT card back in and I'm using it to power the TV. Works flawlessly.

I also had no intention of upgrading to Mojave anyway, so hopefully I can work with this set-up until Mac Pro 2019.
 
So if I upgrade to Mojave with a 120TG and RX560, I'm ****ed?

As far as I can tell you the 120 card will allow you to have the boot picker but there’s no drivers. The finder will be slow and unresponsive. You should be able to navigate around but there’s no native drivers. The 560 isn’t the best choice for Mojave. Apple recommends the 580 but maybe tsialex can offer some feedback here as for native support for the 560. He’s one of the best people on this forum for all things Mac Pro.
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As far as I can tell you the 120 card will allow you to have the boot picker but there’s no drivers. The finder will be slow and unresponsive. You should be able to navigate around but there’s no native drivers. The 560 isn’t the best choice for Mojave. Apple recommends the 580 but maybe tsialex can offer some feedback here as for native support for the 560. He’s one of the best people on this forum for all things Mac Pro.

Edit: the last two posts didn’t refresh on my iPhone. Seems like your current setup will be tolerable based on what tsialex mentioned. Stay on High Sierra for now. It’s the safest place to be at the moment.
 
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