Thought I would give a quick update
So I have not yet updated to Mojave.
But I have updated my Graphics card. On my Mid 2010 Mac Pro (as per sig line below)
I got the:
Sapphire 11265-05-20G Radeon Pulse RX 580 8GB GDDR5 Dual HDMI/ DVI-D/ Dual DP OC with Backplate
https://www.amazon.com/Sapphire-1126.../dp/B06ZZ6FMF8
COMeap Dual Mini 6 Pin to 8 Pin PCI Express Video Card Power Adapter Cable for Mac Pro Tower/Power Mac G5 15-inch(38cm)
https://www.amazon.com/COMeap-Expres...s%2C546&sr=1-4
And for my older Apple Cinema Display (with mini plug)
I got the Cable Matters DisplayPort to Mini DisplayPort Adapter (DP to Mini DP)
https://www.amazon.com/Cable-Matters...0FBPGD3T7JN56J
All toll $207
And I just installed it all which was a breese about 5 to 10 minutes.
The procedure was ---disconnect all power and plugs on back or Mac Pro open up side.
#1 undo the side PCIe slot retainer two finger tight wheels. Pull retainer down and out.
#2 Press the button on the fan housing to slide the fan and Long PCIe retainer bar towards the front
#3 pull out old CPU and the old power supply cabe
#4 push the two new cable 6 pin connectors into the connectors on the mac
#5 push the 8 pin end into the Sapphire
#6 push the Sapphire into the slot
#7 push the fan housing and retainer bar back into position
#8 put the PCIe side slot retainer back on
#9 put the side panel back on the Mac
#10 put the DP to mini Dp cable adaptor on one of the DP ports
#11 plug all the cables back into the back of Mac
Easy peasy
Power on and boot the Mac,,,, black screen for 15- 20 seconds, then slight boot screen flash, and the desktop screen appears
Honestly the no boot screen is a total non issue. Working great so far
Thanks for everyone's help