Civilization V was benchmarked with all settings on high with 4x MSAA enabled. We used the game's built-in Late Game View benchmark. The "Use the GPU for texture decompression" option was checked, but grayed out when testing on the GeForce GTX 260.
Civilization V has major problems running in DX10 mode with the GTX 260; it's not surprising to see the two CPUs tied at 14 fps. Stepping up to the GTX 660 brings the E6850 into playable territory and more than doubles the game's frame rate. The Q6600, however, benefits more -- the quad-core CPU can push the GTX 660 harder than the E6850, despite the latter's clock speed advantage. Overclocking the CPU has no effect; this benchmark is GPU-limited.