Firstly is to introduce myself and my hardwares that make up a 4k gaming rig.

My name is Sam, I am not a professional in computer hardware and my English written language was not good. I just wanted to share the hardware and some problem and difficulty on building a 4 k gaming rig or is it worth to build a 4k gaming rig now?
I am running an Intel I7 4930k ivy-B extreme CPU ocing to 4610mhz. 4 x 8g Quad channel 2800mhz g skill trident x memory, actually running at only 2666mhz no further.
To build a 4k monitor gaming rig the first thing come across my mind is a good graphic card. It must be the top range graphic card between AMD or Nvidia, but Two or more graphic cards required if you running online gaming. I myself have quad cross fire of 2 x R9 295x2 which occupying two Pcie lane with quad CF power. Monitor is cheap Asus PB287Q and a Samsung U28590D 4k monitor. You need to buy at least a 60mhz refresh rate capable monitor with mini DP to DP 1.2 Version cable or DP to DP Cable with DP female to mini DP male Adapter.
4k gaming is slow in online game such as COD , but run smoothly on elite dangerous frontier. . Be prepared of some applications solfware will produce blurry font. Or font and graphic become tiny . I mean really tiny but buy you more screen estate that we seldom use it . It will cause you more trouble in moving the mouse or disappearing of mouse arrow.solution is to increase Windows font DPI size from defaults 100% to 145% . This is the most ideal size for most program . Don't forget to clear image calibration on font and monitor color. It will really help too.
mostly the game on the market is fine for 4k compatible. Some game will not resize to wat you expect in full screen. i mean lower the resolution but never give you full screen mode. Even running with four graphic cards. I also need to lower down some graphic configuration to compete with others else you will find either slower then other or having ghoshting image.
If you found that the program giving you tiny font, you may enlarge your page by pressing CTrL + to make the page bigger without blurring the images on that page. Press CTrL - to make it smaller.
A good 4K monitor you may need to purchase to give you all angle viewing possible , if using the 4k monitor i am using now (CT panel). You will not be able to view completely on different angle, Of cos you need to come out more cash for a better 4k monitor. Usually all games will give your 4K rig refresh rate till 75 hz maximum refresh rate even your 4k panel capable of 100 hz refresh rate.
So far it is more cons then pros by building 4k gaming rig but bare in mind that one thing you will enjoy is the fine detail of graphic that cannot produce by non 4k monitor.
Any experience on 4k gaming and any solution is welcome to post and share in this tread
Thank you

Recently Just bought a Philips 40" BDM4065UC 4K monitor. and i will to share the experience on 4k monitor with such a huge screen size.

ASUS PB287Q - Problem is the cable must use direct mini DP to DP two way 1.2 version cable that ASUS even not provide it. If you using female DP to Mini DP adapter, Asus monitor will blinking but adapter work on all other 4k brand monitor.
Other problem will be the popular 4k issue - Blur font, Tiny font, big fonts, comparability of software, CT panel that limited to viewing angle, require massive graphic power and expensive.

Samsung U28D590D - Same Common issue of 4K monitor but without cable problem.

40" Philips BDM4065UC 4K monitor. - Basically all 4k common issue was solve by using large screen size that suit the 4k resolution, cheap consider the size except massive graphic power is still needed.
Compare the color, intensity, brightness, response time, input ports and the price - No doubt, 40" Philips BDM4065UC 4K monitor is the best of all 4k monitor except the screen size is huge that give inconvenient to PC gamer but solution is to lower down the resolution as screen size will follow and set the screen size format to 1 : 1 is another solution.

This is what i truly experience it and no bias . Thank you .