2 Titan Xs are insane overkill man, just don't. Grab one Titan X or two 980s.
Also, I would grab some standard cas-9 1600Mhz RAM as it will be totally fine..
EDIT:
With one Titan X or two 980s you will be getting about 80-90 fps on all maxed out 1440p, reason is, why would you even need more than that?