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980 is a sideways move imo. Can you wait until 390x is out to see what that offers. Either that or Titan X.
I got another 280x last week for xfire but in my Corsair 550D the heat and noise is just too much.
For gaming at 1440p would I be looking at a 980 for comparable performance?
Have you bought the monitor already? Does it support gsync / freesync?