MSI Radeon 4 GB RX 560 AERO ITX 4G OC AMD GDDR5 Graphics Card in Mac Pro

Make sure that your graphics card works with Mojave

Next, check to see if the graphics card in your Mac Pro is compatible. You can use System Information to find out which graphics card your Mac has:

1. Press and hold the Option key while choosing Apple () menu > System Information.
2. In the sidebar, select Graphics/Displays. If your graphics card is compatible, you see "Supported" next to the Metal entry. You can also note the name of your graphics card and see if it's in the list below.

These specific third-party graphics cards are Metal-capable and compatible with macOS Mojave on Mac Pro (Mid 2010) and Mac Pro (Mid 2012):

• MSI Gaming Radeon RX 560 128-bit 4GB GDRR5
• SAPPHIRE Radeon PULSE RX 580 8GB GDDR5
• SAPPHIRE Radeon HD 7950 Mac Edition
• NVIDIA Quadro K5000 for Mac
• NVIDIA GeForce GTX 680 Mac Edition

Some other third-party graphics cards* based on the following AMD GPU families might also be compatible with macOS Mojave on Mac Pro (Mid 2010) and Mac Pro (Mid 2012):

• AMD Radeon RX 560
• AMD Radeon RX 570
• AMD Radeon RX 580
• AMD Radeon Pro WX 7100
• AMD Radeon RX Vega 56
• AMD Radeon RX Vega 64
• AMD Radeon Pro WX 9100
• AMD Radeon Frontier Edition

If the graphics card in your Mac Pro isn't listed above, you need to install one that's compatible with macOS Mojave. If you need additional help, contact Apple Support.

* Third-party graphics cards vary, so you should check with the vendor of your specific graphics card for compatibility details.

from:

Install macOS 10.14 Mojave on Mac Pro (Mid 2010) and Mac Pro (Mid 2012) - Apple Support

you also need to deal with power issues. the mac provides about 75 watts from the slot and has two 6-pin Aux ports, said to be good for 75 Watts each.

supplying a 150 Watts 8-pin input with a six-pin Aux cord leaves you 75 watts short.

Also, anything not a "Mac-edition" card will not show Boot-up screens -- no screens at all until the login screen.

The important compatibility is with the Big Chip on board. If it is the same as another recommended card, your slightly different card should work just fine. It may have different interfaces.

The amount of RAM on these cards adds a little speedup under certain conditions, because if there is enough RAM, the next screen can be drawn into "off-screen" RAM, and then made active, which allows it to "snap" into view. I don't think any well-known graphics card is "starved" for RAM in a way that would really slow it down.

A single copy of a 4K (3840 by 2160) screen takes about 8M pixels. At 4 bytes per pixel, that's about 32M Bytes. That is 1/32 of ONE Megabyte.

Software like photoshop has always divided its work up into smaller pieces to do transforms on full screens in a piece-by-piece manner to save GPU memory space. At numbers like 16GB, you may not notice the increment to 32GB unless you are doing some really high-powered transformations.