Benchmark Results: Metro 2033 (DX 11)
Although Nvidia’s cards take an early lead in Metro 2033, the AMD Radeon HD 7970s in CrossFire surge forward at 2560x1600 and 5760x1080, demonstrating the strongest advantage with 4x AA turned on.
Meanwhile, the GeForce GTX 690 and GTX 680s in SLI hang very close together, delivering nearly identical performance and showing that you have little to fear from the dual-GPU card’s slightly lower base and Boost clocks.
6990 aren't that hard to find. Back in January before the 7000 series came out, you could easily pick one or two up. I am pretty sure in 6 month, the 690 will be easy to grab.