Install Mojave on 2010 Mac Pro 5.1

That's not the best choice. A full list of compatible cards are:

• 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

I left out the rest because they are only somewhat supported.

Of those above, I believe the only two that were released as official cards for the Mac are the Radeon 7950, and the GeForce GTX 680. That is, they're the only two with a full Mac bios so they support a boot screen. All others require a less capable Mac card installed so it will boot, then the video is handed off to the primary a monitor with the other Metal card.

The 7950 is hard to find, and overpriced. The 680 can be found for about $230 or so on eBay. I have the 680 in my 2010 Mac Pro and it works fine. Either creates more heat than the stock cards you could purchase the Mac with, so expect to hear the fans more often.

If you go for the GTX 680, make sure you look specifically for the Mac Edition. There are lots of of them that are not Mac versions (won't work at all), or have been flashed with a Mac bios. Typically, those won't work for a boot screen. Only after the fact from a stock card that would also have to be installed.

Here's an example of what a real Mac version of the 680 looks like.

I have the AMD Radeon RX580 in my 4.1>5.1 running Mojave. I get no boot screen since it is PC card, not a Mac card.

I had to the Mojave firmware upgrade blink since If I had only the stol GT 120 installed it would not let me even start the Mojave install process and if I had both the 120 and 580 cards install the MP would not boot.

Just how difficult was it to install Mojave?

What makes you think it will not be compatible with "Mac Cinema Display" (which one(s))?