Titans are a waste of money, unless you are running triple screen 1440p monitors. And even then they don't help *that much*. Even with new gen games coming out 3GB is enough. Just look at Last Light 7680x1440 benchmarks. By the time 3GB isn't enough, the "raw power" of a Titan won't be enough either (think 3-5 years), ergo Titans are a waste.
With that budget the only snart options for GPUS are SLI 780s, or wait for AMD cards (which is the more intelligent choice).