As the subject of this post says, I’m wondering which expansion card will provide better speeds and quality.
Are you talking about HDMI vs DisplayPort?
As I understand it, the signal coming out of the USB ports is a DisplayPort one. The DisplayPort card is a fairly simple one that just forwards the signal unchanged. The HDMI card, on the other hand, has to do a lot of complex conversion stuff to format the results for HDMI.
So if you can use either of them, the DisplayPort one might be the better choice.
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is your FW AMD and running Linux?
It probably doesn’t affect us in present days since the hdmi expansion card supports HDMI 2.0b.
But I personally would choose to use DisplayPort if I can 
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thank you
The laptop internally only supports DisplayPort.
The DisplayPort card simply relays the DisplayPort signals from the laptop. It’s capabilities match what the laptop (and the processor in the laptop) supports.
The HDMI card on the other hand receives a DisplayPort signal from the laptop and runs it through a chip that translates DisplayPort signals into HDMI signals. That means that it is limited to whatever the laptop supports or what the chip in the card supports, whichever is lower.
All Framework Laptops support at least 25.92 Gbps of display bandwidth. Some may support higher (but I’ve seen some conflicting info). That means that the DisplayPort cards support 25.92 Gbps of display bandwidth.
The HDMI cards on the other hand are limited to a lower 14.4 Gbps because that’s all the internal chip of those cards supports. If a display needs more than 14.4 Gbps then the DisplayPort card will be necessary in order to run the display at full speed/quality.
Furthermore the HDMI card does not support DSC whereas the laptop (and by extension DisplayPort cards) do. DSC is a lossy compression algorithm, which means it makes a sacrifice to quality to dramatically reduce the required bandwidth (allowing something that would otherwise require 77 Gbps to work properly just with a very minor reduction in quality). DSC has been praised for the quality reduction being so small that most people can’t tell even in a side by side comparison. So the lack of DSC further increases the difference between HDMI and DisplayPort cards.
Even if/when an HDMI 2.1 card comes out I’m not sure it will affect us.
Like I mentioned above Framework laptops don’t support HDMI but instead rely on a chip in the expansion card to translate DisplayPort signals to HDMI.
From what I’ve read Intel GPUs (at least some of them) aren’t affected by the issue you mentioned because the GPU core doesn’t support HDMI but instead has a separate chip to translate DisplayPort signals to HDMI.
The HDMI Forum objects to open source drivers that support HDMI 2.1. However they have no objection to having open source drivers that only support DisplayPort and running that DisplayPort signal through a DisplayPort to HDMI translator chip (and the translator chip has its own closed source firmware).
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