2 GeForce GTX 690 vs. GeForce GTX 680 SLI

In one corner, the fastest single GPU card in the markets at the moment which is priced 500$, and in the other corner, nVidia's dual GK104 core GTX 690, priced 1000$.

It's the same price to buy either a 690, or a 680 SLI, but let's see which one performs better.

In the chart, we can see that GTX 690 is basically two GTX 680's on the same card. The core of 680 is doubled and placed on the 690. The only little difference between these two cards is that 690 has a higher GPU frequency as we can see above. Though, it's less power consuming to run a 690 than 680 SLI since 690 consumes a maximum of 300W power whereas 680 consumes 195W. Running SLI also means you'll need more cooling than running a single 690.

All being said, it's time to compare the performances of these cards. (Benchmarks taken from legitreviews.com)

As we see in the benchmarks, 680 SLI and 690 are very close to each other in every single one. It's no surprise to be honest, since both of the setups share nearly the exact values when we look at the charts. The difference between them isn't even close to be noticeable in a daily scenario. 

That being the case, I believe it would be more logical to buy a 690, since it's more open to upgrade when you have the money, (SLI 690) it's easy to cool, and it takes up less power. Even though the 680 SLI came in front in most of the benchmarks, we can see that the difference varies from 0.1 to 2 FPS maximum. Considering the advantages you get from buying a 690 compared to 680's small performance advantage, the good choice would be to buy a 690, especially if you are considering high resolutions. (2560x1600)

All in all, choosing either 680 SLI or 690 won't really make a difference at all, but you'd be saving some power and making an investment for the future by buying the 690.