Hardware.Info posted Asus PG27AQ review: 4K gaming ready
A quote from the article:
This year both AMD and Nvidia will introduce new GPU architectures, that should be a giant leap forwards in terms of performance, partly because of the switch to a smaller production process. This means that 4K gaming, gaming at a resolution of 3840x2160, will be possible at higher frame rates meaning it is more interesting to play at this resolution. Asus already introduced a new monitor to be ready for this: the RoG Switft PG27AQ. An ultra hd monitor with an IPS-panel and support for G-sync. You can find our test results in this article.Asus PG27AQ review: 4K gaming ready @ Hardware.Info
For now, in order to game at 4K resolution with acceptable frame rates you need at least two of the fastest, most expensive, graphics cards available now; like the Nvidia GeForce GTX 980 Ti. Even then you will need to turn down the graphics settings in modern games in order to have a fluid experience. As there are not a lot of people that spend this much money on their graphics cards, it is safe to say that 4K gaming is more of a promise than a reality in this day and age.