With two GTX 670 graphics cards we can save more than 200 euros and gain similar performance to GTX 680 SLI. We need to overclock those GTX 670 cards off course, but for those who do not want to deal with overclocking, two GTX 670 Phantom cards are a viable option. The GTX 670 Phantom sports a factory overclocked GPU which is set at 1006MHz, and this is exactly the same clock used on the GTX 680.
Performance of a single GTX 670 Phantom graphics card is close to that of GTX 680 but not the same, mainly because GTX 680 has 1536 CUDA cores while GTX 670 has 1344. We haven't noticed any significant difference in games except in tessellation heavy tests. Memory subsystems on both cards are the same 256-bit ones and each card has 2GB of GDDR5 memory. As expected, GTX 670 SLI power consumption is a bit lower compared to the GTX 680 SLI.
The performance boost we got with SLI is great. We could play any game at 2560x1600. Additional overclocking is similar to what we scored with a single GTX 670 Phantom card.
The only thing we did not like with GTX 670 Phantom SLI is fan noise. The fans are not too loud but are not comfortable either. Two GTX 680 cards in SLI are a bit quieter compared to the GTX 670 Phantom SLI.
If you value quiet operation and power consumption, the best decision would be to go for GTX 690. 1000 euro buys two GTX 680 cards, or a single GTX 690. At the same time, 760 euro for two GTX 670 Phantom cards sounds like a much more reasonable choice for most of us.
In short we just showed that performance-wise, two factory overclocked GTX 670 Phantom cards can hold their own against the GTX 680 SLI, and they are certainly a more affordable option. Bear in mind though that Phantom cooling is three slots wide.