Mac Pro 6,1 (2013) and Samsung CRG9 49" Monitor
Need some advice. I have a 2013 Mac Pro with D500 GPU's and a Samsung CRG9 49" Monitor. The Mac Pro won't utilize the full 5120x1440 resolution of the monitor. I have used SwitchResX and oddly, I can get the full resolution on HDMI but not displayport but the image is fuzzy and not really usable. I can use dual display port cables to the monitor and configure PBP and that provides a sharp image of dual 2560x1440 monitors but application windows need to be one one or the other side, they cannot 'span' the two virtual monitors, another problem.
I even bought a new Mac Mini with TB3 that is supposed to support 5120x2880 to drive this monitor. Apple confirmed that it would support the monitor before I bought it and it does, but it is also fuzzy. No better than the TB2 on my Mac Pro, so I returned it.
What I want to do is use a eGPU to enable full 5120x1440, sharp resolution on monitor and to speed up video rendering (I am not a gamer). Has anyone done this? Can anyone tell me if I can get that sharp 5120x1440 resolution on the Samsung with my TB2 Mac Pro?
Mac mini 2018 cannot do width > 4096 with single connection displays. The LG UltraFine 5K display uses two DisplayPort connections over Thunderbolt to do 5120x2880 (each connection is 2560x2880 but it appears as a single connection to the user, unlike PBP).
HDMI output has less bandwidth than DisplayPort 1.2 but 5120x1440 requires less bandwidth than 4K so it shouldn't be a problem. You may have been using a 5120x1440 framebuffer but the output signal could be 3840x1080. macOS only shows you the framebuffer resolution and pixel format. It doesn't show the output resolution and pixel format. For output resolution, use SwitchResX to view the timing info of the current resolution (double click the current resolution) or use the AGDCDiagnose command (it shows connection info but only shows output resolution and pixel format for AMD graphics).
The new version of macOS (Big Sur) may add > 4096 width for Intel Kaby Lake graphics (but not Intel Coffee Lake which is an updated version of Kaby Lake in the Mac mini). Intel Ice Lake graphics (10th gen CPU, Gen11 graphics) does not have the 4096 width limit in Catalina.
I don't know if Big Sur fixes Mac Pro Dxxx AMD graphics.
Any eGPU should allow single connection 5120x1440 mode.
You can enable display spanning of windows across displays by disabling the "Displays have separate spaces" option in Mission Control preferences panel in System Preferences.app.
Another question, so I followed your instructions and captured the timing data on my current resolution, 2560x1440 and I want to create a custom resolution for 5120x1440 single cable. How do I use the timing information I captured to create the new custom resolution? Do I have to disable SIP as well?
@ca_sunshine, the display has the 5120x1440 timing already in its EDID so you don't need to add it. Your problem is not the timing. The timing is perfectly valid. Your problem is the GPU doesn't support the timing correctly.
The Mac Pro's HDMI port only support HDMI 1.4 - it's not enough to support 5120x1440 60Hz. Maybe it could support 5120x1440 30Hz? You could try adding a timing for that if it's not included in the EDID. But the GPU itself probably doesn't like the 5120 width. Well, I guess you can try. Also, post a photo of the result (for HDMI and DisplayPort).
In SwitchResX, create timings in the Custom Timings tab. Use CVT-RB calculation. Then type Command-S to save. Then press the Activate Immediately button. Then check the tabs to see if the timing was added. If so, then try the timing.