I can’t argue with your experience; thank you so much for also sending me the part number of the cable!
Did you also install the B173ZAN06.1? For the 120hz monitor, I think I have an idea of what’s going on with macOS:
From my experience with Nvidia graphics, I can tell you that the problem with the capped framerate in macOS is likely coming from the Radeon driver in System/Library/Extensions.
Somewhere within the specific framebuffer that attaches to the 5700m (and possibly CoreDisplay), a max pixel clock rate is being defined (in hz). This max pixel clock rate is too low and capping your frame rate for the 4k monitor to 60hz. You have to increase the pixel clock limit to whatever will give you 120hz.
This person created what appears to be a simple patch for Nvidia/Intel graphics cards, and I have a feeling that AMD cards will require a similar patch.
For my Nvidia card, the max rate was 165MHz, but it may be different for Radeon cards.
165 MHz -> 165x10^6 Hz -> 165000000 Hz
Awesome to hear that regarding the monitor, but knowing you and I, we both want our high refresh rate if it's possible 😆. If I can’t purchase a cable I’ll just go with the 6.0.
Funny enough, I was about to recommend SwitchResX to calculate the limit for the pixel clock rate!
(If you disable HiDPI, I would imagine that you’d be able to achieve 120HZ refresh rate at 1080p.)
I won’t be very helpful right now as I don’t have a 4k monitor, or anything with a super high refresh rate, but try setting up some custom resolutions/refresh rates in SwitchResX to see where the pixel clock limit occurs. (the point where you won’t be able to use the custom resolution/refresh rate)
Whatever that number ends up being must be coded somewhere within the Radeon Framebuffer, and I’d assume that you should be able to just change it to something higher to increase the refresh rate.
Wow @kingo132, you've really been killing it (you're a video driver expert)! I've still got to purchase a 4K panel myself before I can see your progress.
In terms of progress that I've made, I don't know if this is helpful at all but I figured that I'd share it:
Under Windows, I've been messing with the 10-band EQ in the "Realtek Audio Console," and figured out how to tune the speakers to NOT sound like an old analog radio.
Perhaps when it's time to fix the audio, if there's a way to add some DSP work to the audio signal with a band equalizer, maybe we can create two versions of the codec patch: original and processed (or I guess you could also just use the Boom app).