Seems like you've narrowed things down a bit with the process of elimination. Glad you are getting a new machine. Me too..very soon. 

SLI......some folks use it. Some don't.  For actual performance though the rule of thumb is that a single top end card is better than two low or mid grade cards in SLI.  Like Silverblade said, it's not worth the hassle if you want performance.

I think it appeals to gamers who view their machines like souped up cars.

I personally cannot wait to do an actual Vue render with atmospherics and lighting and godrays and all the other stuff I've avoided because my machine can't handle it.  

Good luck Peg.