nope, still 8 GB of RAM, RAM doesn't stack
power consumes should hover around 2x the TDP, might be more (probably)
performance most likely would be 1.5x - 1.7x the one u have now
also, remember, even though Nvidia optimize the SLI tech, most devs don't want the hassle of doing that, so in some games, u can get a performance increase, in some games, it'll play just like u're having a single GPU, in other games, u might even have a performance decrease
SLI support on games are still pretty unreliable so unless u only play few games, and all of those supports SLI, then i wouldn't do that