If you have infinite budgets, you might as well get the 2011 slot. The 3960x is Intel's best retail processor but it is more than $1000 last I checked just for that one piece. The motherboards will be twice as expensive, yadda yadda yadda.
SLIing is not a great idea for graphics related things anyway, but 2011 does that better.
Really, if you are a gamer I would say that you should just use 1155 and 1x of the best video card you can afford.
If you have infinite money and want to use the computer for something useful that isn't graphics related like folding@home where you use the power of your graphics cards to help cure cancer and stuff, then go for the 2011 and as many GTX 680s as you can afford and/or fit in the board.