The fact that you think buying a Titan Z, and a $1k monitor is what you need just to play 4K, is why you aren't going to need to play 4K.
I can go out and buy a 4690k, a single GTX 970, a $400 4K monitor, and play most modern games on medium settings, and get 30-40 FPS.
A Titan Z isn't for gaming anyways. And I highly doubt that BenQ monitor is even good.