So, after much searching, it turns out Apple won't allow the MacPro 2013 to run 5120x1440 @ 60hz or more over TB2 despite the built in GPU being capable of it, and that Thunderbolt 2 also has plenty of bandwidth for it.
Why? Some have traced the root cause to the way Apple implemented Audio thru DP connections.
New M1 based Apples are having the same issues, despite 5120x1440 requiring less bandwidth than 4k @ 60hz.
This leaves me with an option that frankly is unappealing. I can use the Side by Side to logically split the monitor into two separate 2560x1440 monitors. I can drive each side with a single cable.
I'm using 1x DP 1.4 cable for my Gaming PC. This leaves with the 2nd DP input for one side, and a HDMI for the other side.
But to switch back and forth will probably more trickery than just switching inputs.
Why? Some have traced the root cause to the way Apple implemented Audio thru DP connections.
New M1 based Apples are having the same issues, despite 5120x1440 requiring less bandwidth than 4k @ 60hz.
This leaves me with an option that frankly is unappealing. I can use the Side by Side to logically split the monitor into two separate 2560x1440 monitors. I can drive each side with a single cable.
I'm using 1x DP 1.4 cable for my Gaming PC. This leaves with the 2nd DP input for one side, and a HDMI for the other side.
But to switch back and forth will probably more trickery than just switching inputs.