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It's always the question on anyones lips.... to upgrade or not?? I was in the same position going from a 670 to a 780.
Questions you ask yourself is are you happy with the performance you have now? If yes wait? If no then SLI/Crossfire or get a new card.
Waiting is pointless cause you could wait and then they might say we are working on blah blah and it will be out in 6-12 months. Tech moves quickly!