Metro 2033 stands among the generation of DirectX 11 games that showcase the graphics card as being the limiting factor. CPU utilization is at 100% with a single-core CPU, but then again, so is GPU utilization. Increasing the number of CPU cores and overclocking does not yield any higher frame rates.
To produce measureable frame rate impacts, we had to decrease the anti-aliasing to a gentler AAA mode (analytical anti-aliasing), instead of the hardware-taxing MSAA setting. Graphics memory reached its peak at 761 MB. To get better frame rates, we can only recommend a better graphics card, which is why we tested this game with the AMD Radeon HD 5870.
In extended benchmarking, we used both a single AMD Radeon HD 5870 as well as two of them in CrossFire mode. With these test results, we can elaborate a bit more on the CPU's role. The processor is still not a big factor, but it becomes relevant again with CrossFire activated. If you're going to use two graphic cards, at least pick a dual-core CPU. If you have a single-core chip, you could skip the second graphics card, as performance will be almost halved. Four processing cores and extra clock rate via overclocking is overkill, though. As long as you have a sufficiently fast dual-core CPU, then the rest will be up to the graphic cards.