IMHO, there is no need to spend ~$1K just because you have it and it is always better to get the best single card than start off w/SLI; less issues of heat (going blower style or good airflow in the case), power (got a quality 650+ watt PSU?), driver optimizations ( more so for newer games - not talking about stutter - talking about scaling) and upgrading (you'd need to upgrade to another SLI setup or down/side grade). bottom line; a single 780 will handle every game @1080 so there is no need to go further
but i have to admit to being biased towards the 780. thank god nvidia but a wider than 256 bit bus on a card after a year and a half that doesn't cost an arm and a leg. but bank the $350 difference and use that toward another 780 later.