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It depends what you expect from it, but as long as you don't expect a specific nuumber of fps for across the board for every title, then I don't see why it can't at least last another year, maybe two.
By the time the 570 struggles to play the latest games you'll be able to buy another one pretty cheapily for an SLI setup.
Depends if you want efficiency over speed. I doubt there'll be an affordable card out in the next 2-3 years which would surpass twin 570's for speed.