I know Apple says 6-4K or 2-5K or 2-XDR, but can it do 1-XDR and 2-5K?
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I just answered my own question... thanks. Yes, this card can run 2-5Ks and 1-XDR.
If the 5Ks are LG UltraFine 5K, then they both must run at 4K.
The LG UltraFine 5K requires two DisplayPort signals from a Thunderbolt controller.
The XDR requires two DisplayPort signals from a Thunderbolt controller (when using a GPU like the 580X that doesn't support Display Stream Compression (DSC)).
Each Thunderbolt controller only gets two DisplayPort signals.
The Mac Pro has one Thunderbolt controller on the I/O card, and another on the top of the Mac Pro.
The 580X does not have any Thunderbolt controllers like the other MPX GPUs.
Therefore, one display can connect to the top, and another can connect to the I/O card. Two 4K displays can be connected to the HDMI ports (maybe?).
You can use SwitchResX to verify the output resolution of each display (nowhere else in macOS is this info available). Double click the current resolution in the Current Resolutions tab of the display in SwitchResX to view Pixel Clock, Active, Scan rate, Scale to.
