What would you recommend and why?

[wwoneo]

I am putting together a new system and am trying to decide what would be a better choice.

Should I get NVIDIA GeForce GTX 970 - 4GB - EVGA Superclocked x2 (dual cards), or should I go with (1) NVIDIA GeForce GTX Titan Z - 12GBSingle Card?

Note that I could get dual cards for 700$ less than the 1 GTX Titan Z single card. How much of a difference do you guys think it would make?

What are the pros and cons of getting each?