buddy two titan z?????? hmmmm this is some serious stuff. Get corsair ax1200i or the newly launched ax1500. Titan z need 600 watts to work under full load. so AX1500 would be the best choice for you....
GeForce GTX 780 Ti - On your average system the card requires you to have a 550 Watt power supply unit.
GeForce GTX 780 Ti 2-way SLI - On your average system the cards require you to have a 800 Watt power supply unit as minimum.
GeForce GTX 780 Ti 3-way SLI - On your average system the cards require you to have a 1200 Watt power supply unit as minimum.
I have to assume that the 400 watt jump from 800 to 1200 is because there's slim pickins in the 1100 range....
Titan z is a complete potato GPU. It has no real reason or purpose beyond its existence. Its twice as expensive as a r9 295x2 , offers lower performance compared to it ( and even compared to 780ti sli)
-either buy 2r9 295x2 which curently hold the crown for best (dual)GPU card
-go for 4 gtx780ti which are more ore less the same perfirmance
The real world performance beteewn these 2 configs is set by the driver performance and efectiveness.
Titan Z is an engineering failure. Assuming you even require 2 of these GPUs you'd be better off with 2x R9295x2. There is a higher power consumption but with what your system takes up it won't really matter anyway. I think 1300-1500W would be enough but I'm not sure and aren't too interested personally.
As for the PSU the best is the corsair 1500ax
-its 1500w ( considering dual r9 295x2 or quad gtx780ti have 1000w TDP and a intel EE has 140w youll have 1140 leaving 360w for other things. Also youll never reach full usage of CPU/GPU in gaming unles you run stresing tests as futuremark and wprime at same time)
-its made specially for OCers meaning it has special features such as holding 1650w if needed
-only psu wit 80+ titanium certification(93% efficiency on 10% to 90% load)
Really it would be a crime not to take this PSU for such a configuration.Its the best . 1st at efficiency/performance and techpower up backs it up.