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Loosely, the GeForce GTX 770 is to the GTX 680 as the Radeon HD 7970 GHz Edition is to the original 7970. It's a higher bin of an old chip likely made possible by process node improvements, and roughly ties the 7970 GHz Edition in gaming performance.
The usual GK104 versus Tahiti comparisons still apply. The GTX 770 loses some energy efficiency due to essentially being overclocked, but it's still more energy efficient than the 7970 GHz Edition simply because Tahiti was something of a power hog. Meanwhile, the GTX 770 is very much a gaming-focused card and lacks the GPU compute capabilities of the 7970.
What is a big deal, though, is the price tag: $400. For comparison, New Egg only has one GeForce GTX 680 meaningfully under $450. The nearest AMD competitor, the Radeon HD 7970 GHz Edition, starts at $450 before rebates. AMD will likely change that quickly and cut non-GHz 7970 prices, too, but until then, at $400, the GTX 770 is the card to get.
For quite some time now, getting anything faster than a GeForce GTX 660 or Radeon HD 7870 has meant that performance per dollar dropped substantially. Above a Radeon HD 7950 Boost at $300, it got even worse. A GeForce GTX 770 at $400 gives you a decent choice at that price and will likely push some other cards down, too. While the GeForce GTX 780 and Titan still offer terrible performance per dollar, they're a matter of, if you want that kind of performance, you either pay what it costs or do without.