I don't have SLI. Only a single GTX 680
Sorry to say Meiny, but regardless of your system, you are still going to receive low fps when there's plenty of people around. This engine is a piece of junk. The engine bottlenecks.
Please save yourself a lot of time, and either A) Lower the visible character limit to medium or low, and turn shadows off. Or: B) Save yourself the investment of time in this game, and move to an MMO that respects and supports their community, whilst creating an efficient, quality game.
Refer to my old thread on performance if you wish: http://www.swtor.com/community/showthread.php?t=507316