They're 60Hz. You won't get frame rates much higher that 60 on a triple setup, so it's not worth spending more. You also NEED the viewing angles of IPS, so you're pretty much stuck with 60Hz.
Response time's effect is a myth. 8ms would be more than enough for frame rates of 120hz and under. Most of the industry tests are different between manufacturers, so one 2ms monitor could measure as a 5ms by another company's standard anyway.
The human eye can't tell a difference of 6ms. If you were to sit someone down and show them a 2ms, 5ms, and 8ms monitor at 60Hz, the chances of them identifying the monitors correctly would rely solely on luck.
Response time is an almost meaningless figure to look at when buying monitors, so long as it's no higher than 16ms for a 60hz monitor, there will be no detectable difference.
A Titan Z will run a triple setup, just not as well as SLi GTX 980s, and it will cost more. The Titan X is a single GPU card, so unless it is an absolutely extreme piece of technology, it won't run a triple setup on it's own - you'll need two.
27" is too big for a triple display. The edge monitors leave your peripheral vision, and you have to bend the outer screens to such an angle that you get massive distortion. 24" is the biggest you can go.