Your benchmarks are using "custom settings." That's not very helpful. Playing games and "maxing" games at 4K are 2 different things. And with todays hardware we aren't quite there.
The rig used in these benchmarks is a i7 4690X at 4.6 GHz and 32 GB of RAM at 1866 MHz. That computer with a Titan Z costs well over $5,000. That runs Battlefield 4 at a 47fps average. The only thing that gets it over 60fps is 2 AMD R9 295X2's. (Crazy thing is that is about the same price as 1 Titan Z. Silly Nvidia) Crysis 3 only gets to 30 fps no matter how much money you throw at it. I'm gonna say we aren't ready for 4K gaming quite yet.
What if I told you that in gaming i7 4960x (1500USD) performs the same as 7 4770k (330USD) FACT
RAM clock doesn't matter AT ALL.
So i7 4770k, 8GB 1600Ghz, GTX 780 sli will perform the same as i7 4960x , 32GB 1866Ghz, GTX 780 sli.
And buying GTX Titan Z would be a complete madness as for the half of that money I will make a triple GTX780 sli tat will ra*pe TitanZ
I dont know if you chose the best game to prove your point, but I agree that for gaming the 4770K or 4970K are more than capable. (The 4960X does not cost $1500 though) Outside of gaming the 4960X has many advantages so your statement that the 2 will perform the same is false. But for gaming only purposes you are correct. And I only mentioned the RAM clock speeds because it was relevant to the specs of the rig used in the benchmarks I showed.
And the Titan Z does have a place. (As does the 295X2) I almost built a mini ITX computer and would have used that card. It is perfect for that since there is no room for 3 780 ti's. I chose to go a different route however.