Performance results: Power
Few people use their PC exclusively for gaming, so it makes sense to test both idle performance and performance under 3D load. Idle performance is close to what you'll see from these cards when you run normal desktop applications on your system.
Of the three cards we tested, the Sapphire model consumed the least power when idling, but it also drew the most power under load. The idle power difference between the HD 7970 and the Asus GTX 680 is minimal, however. Load power consumption differences are more substantial, but even the 18W difference there won't greatly affect your power bill.
The Sapphire card was a little louder than the Asus card, but a little quieter than the EVGA GTX 680 Classified. All three cards were considerably less noisy than the previous generation's high-end cards, however. This is partly due to their improved power efficiency: These cards just don't get as hot as their predecessors did. In addition, the manufacturers have worked to tune their cooling systems to minimize more-noticeable, higher-frequency noise.
3DMark 2011 and Unigine Heaven
These two synthetic benchmarks make somewhat harsher demands on GPUs than most games do, though the type of load doesn't always reflect what modern games are doing. Think of these benchmarks as tests of potential, rather than real, performance.
The Asus GTX 680 DCII TOP won out in 3DMark 2011 by a wide margin. The differences in the Unigine Heaven test became less noticeable once we turned on antialiasing. Still, the results for the two GTX 680 cards were pretty close whether antialiasing was turned on or off, and both of them eked out wins over the Sapphire card.
When we look at the results of actual game testing, we see that performance differences tended to vary from game to game, depending on the kind of game load presented. Each game in our test suite approaches 3D rendering chores in its own way.
The Radeon HD 7970 did fairly well on Crysis 2. Notably, enabling hardware tessellation in Crysis 2 flipped the result, with the Nvidia GPUs outperforming the AMD. But Crysis 2's tessellation isn't very smart, which prevent it from being a very representative example of how most games use tessellation.
The Asus TOP card pretty much cleaned up on Shogun 2. Shogun 2's heavy use of graphics shaders put the Asus card's high core clock speed to good use.
DiRT Showdown uses GPU compute for its advanced lighting engine, particularly when handling global illumination. The differences in GPU compute performance were especially noticeable in this game test. We can't predict how many future games will use the techniques that DiRT Showdown employs, but it is an interesting example. The Radeon HD 7970 demonstrated a clear and unambiguous performance advantage in this game.
The older DiRT 3 uses more-traditional DirectX 11 rendering techniques. At our test resolution, it also seems to be CPU-bound, and the result was a dead heat.
Metro 2033 is a massive system hog, as the low overall frame rates on this test indicate. AMD earned a technical knockout here, but the differences overall weren't that large.
Batman: Arkham City is a much more conventional game, and our test cards were clearly up to the task of running it well. Once again, the Sapphire captured first place (by a margin of 3 frames per second), but all of the cards turned in frame rates well over 60 fps, so the practical differene in results is minimal.
All three cards performed well on most games, and the differences between them were generally small. The outlier here involved DiRT Showdown--but elsewhere the results were pretty even.
The EVGA GTX 680 Classified is an intriguing but ultimately imperfect card. It includes 4GB of video memory, so if you plan on running three 1080p monitors using Nivida's 3D Vision stereoscopic display technology, this card might be a good choice. On the other hand, the extra height makes it problematic to install in many cases--and it's a little noisier than the Asus card, too. The dual 8-pin power connectors might mean that you can manually overclock it to a greater extent, particularly with EVGA's excellent Precision X overclocking software; but many users may feel skittish about overclocking a GPU that's already pushed pretty hard.
At $475, the Sapphire Radeon HD 7970 Dual X OC wins the crown for best price/performance ratio. However, it consumes a little more power and makes a little noise than the Asus GTX 680 DCII TOP. I would be inclined to go with the Asus card based on noise levels alone. The massive Asus GTX 680 DCII TOP is about as quiet a high-end card as I've ever heard. And at $550, it costs substantially less than EVGA's Classified card. If you want the performance, but not the noise, of a high-end GPU, the Asus GTX 680 DCII TOP is a great choice.