I honestly think 560ti SLI is your best bet, you'll get performance that surpasses the current 680. there's the occasional headache of some game not supporting SLI configurations correctly, but most of those are quickly resolved and you can always come back here to ask questions
as for buying a new card, I would definitely wait for the 700 series, however, do note that Nvidia does not have a great history of dropping prices. if you look back to when the 600 series came out, the price of the 500 dropped a little bit, but then were either re-branded into the 600 series, or production simply stopped.