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my R9 280 working at 2013? and dont broken, If buy today needs looking the state of the video card, so that there is no smell of textolite, then it is understood that it did not bask more than 85?and coolers state. Profit is achieved faster than expensive cards.But this is a personal opinion
Of course most of old cards are still good for mining, but do not forget about energy effeciency: new cards on 14-16nm techproccess are 1.5 times less power at the same computational power. And if you have limited electricity outlet so now it's time to change old cards to new