Say, I want a 5K monitor and make sure it would be as snappy as possible. What would be my desktop video card of choice? Price does not matter much, but I do not think it is smart to invest into 3d acceleration features that Qubes cannot use anyway.
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I also have this requirement.
The other question I have is do we need to passthrough the dedicated GPU card to let Qubes OS use it to display? Because my current laptop only use iGPU to display.
Noo, unfortunately I do not think gpu passthrough for sys-gui is a game-changer 
in AppVMs we still have software rendering and performance advantage of passing bitmaps in “accelerated” fashion is marginal if does exist at all. So no good use for GPU at all, except screensaver maybe 
This is my opinion too. So I want to use the best CPU which can work on Qubes OS. AMD Ryzen 9 5950X in this HCL is the best I have found.
We also need a dedicated GPU if the CPU we choose doesn’t have iGPU. I suppose we can use a cheapest one if screen is rendered only by CPU?
App qubes use a software-only (CPU-based) implementation of OpenGL, which may be good enough for basic games and applications.
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