Doing some comparison of the Asus 4K monitor versus the Eizo Surround setup. I could not directly put the setups next to each other due to the incredibly short cable distance allowed under 4k 60 Hz.
First thing I noticed as I turned on the power switch is just terrible black levels, IPS glow and the bezel pinching the corners of the display causing back light bleed. The picture below is a bit exaggerated like normal, but it is still very apparent in real viewing:
A close up of the worst corner, bottom left:
White's were all blotchy/cloudy:
Games look great with the resolution and clarity, but here you can see quite bit of motion blur, especially with the people in the stands.
The deadly AFK smooth camera spin of Skyrim. Extremely difficult test for motion blur. Unfortunately the 4K Asus does about the worst I've ever seen in this test:
In real world viewing, when you are panning the camera around in something like Skyrim or an FPS, you really can't see anything until you stop the movement due to the smearing. Obviously I could not recommend the monitor for gaming.
I will say though, on bright static images, the 4K display is quite gorgeous! 4K resolution is the future, it's just currently in a very immature state.
The 3x Eizo setup handily serves the 4K it's butt on a platter for gaming. Like all IPS displays, they will be destroyed by the black's and contrast ratios of VA panels like the Eizo. The Eizo FG2421 isn't only a VA panel, it is an extremely good VA panel that puts out some of the best black and contrast ratios in the business.
Switching between the Eizo, the 4K IPs, the random TN panels around here is just a night and day difference. Once you get used to super blacks and contrast ratios and no glowing screens, it's hard to go back! There is a down-side with the black crush/gamma shift, but it's a small price to pay. Plus the Eizo's strobing backlight motion clarity, it's just no contest.
Add onto the fact 120 Hz 4K monitors could be a half a decade or more away, I could see myself hanging onto this 3x Eizo setup for quite a long time. It does everything really well. I may even try and get 5x1 working with AMD.