I'm going to hate saying this because im a HUGE Nivida fan, but if your going 12k gaming (3, 4k monitoirs or 11,520 x 2,160 pixels) it is better to use AMD GPU's.
The reason why they are using AMD GPUs instead of NVIDIA GPUs is simple, at the time of writing this post, the PN-K321 (best 4k screen in the currently in the market) does not work with NVIDIA GPUs at 4K @ 60 Hz due to NVIDIA's artificially crippled driver.
In a pointless attempt to protect the revenues of their very expensive professional Quardro GPUs, NVIDIA artifically cripples their Windows (assuming this is your OS) driver to prevent users from using features like Surround 2x1, 2x2 configurations, 10-bit color and multiple display stereoscopic 3D in OpenGL (Quad Buffer Stereo). All Geforce cards are capable of these features and they are accessible when using the Linux GeForce driver but they are artificially disabled in the Windows driver.
Due to silicon limitations, this display requires DisplayPort MST to operate at 4K @ 60 Hz. The display actually appears as two tiled 1920x2160 monitors which is why this monitor is capable of doing 4K @ 60 Hz over 2 HDMI cables.
With the introduction of this monitor, NVIDIA was left with a choice, either support Surround 2x1, 2x2 configurations properly so anyone with any pair of monitors could play a 3D game with any variety of 2 or 4 monitors or they could write some sort of hack in the driver to support these types of monitors specifically while avoiding giving Windows users 2x1 and 2x2 Surround support.
NVIDIA is the lone GPU maker without 2x1 and 2x2 monitor configuration support. AMD has supported it forever with Eyefinity and now even Intel supports these configurations with their integrated GPUs using their Collage feature.
So you can probably guess what NVIDIA decided to do, instead of supporting Surround 2x1 properly, they decided to hack their drivers. They created an EDID white-list so they could detect these kinds of monitors and support their unique 2x1 capability while still disabling general Surround 2x1 support with any pair of monitors.
NVIDIA had an pre-production version of this display and updated their driver based on that. However when Sharp finally shipped this monitor, they changed the EDID data from the pre-production display. This change caused the display to fail the NVIDIA EDID whitelist check and not allow it to operate at 4K @ 60 Hz. So now NVIDIA is in the process of adding the correct EDID data to the white-list in the driver and soon the monitor will finally work with NVIDIA GPUs.
NVIDIA could have avoided all this by just giving everyone proper 2x1 and 2x2 surround support.
This comment is a summary of the following massive 9 page thread with comments directly from NVIDIA confirming the above:
https://forums.geforce.com/default/topic/539645/nvidia-surround/2-monitor-gaming-/1
So, I said it, sorry to ruin your dreams, but its fact and i can't fight that :/