Thats a very difficult question to answer, obviously you don't 'need' any GPU at all it's not exactly a human right. It's simply something that you want and desire is a difficult thing to justify objectively.
People play at 1080p with far less hardware and i'm sure other people have far more, as we all know you can't have too much overkill! I personally have two 780's running a 1440p panel and if you try really hard with the eye candy in certain games you can hold them back. While on other easy running games like Grid or Dirt say just one 780 will achieve way over 60fps max settings @1440p. But when I buy any hardware, aesthetics, quality, noise levels and block compatibility are considered over shear price/performance as well as brand loyalty, another one of those irrational factors.
Now the big point to consider for yourself is are you actually buying for 1080p or 1440p. If it's 1440p you'd be far better off starting with a 780Ti or 290x rather than ending up with two 770's or 280x's in a years time when they are obsolete and worse performing by comparison. If your buying for 1080p however looking slightly lower down might be a good idea, you can always upgrade again in the future. What do you currently have? Is it liveable with for a bit longer until you decide to go either way?
I understand that your just looking for a bit of practical advice but most of the people with experience of high end hardware I bet rarely end up taking the most sensible route. Don't get stuck in a constant upgrade loop, unless you want to, depends if your a gamer or a hardware nut at the end of the day.
JR
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