http://www.techspot.com/article/255-battlefield-bad-company2-performance/page7.html
Here is the same Core i7 920 processor with two cores disabled as well as HyperThreading. As you can see neither core is maxed out, but the CPU utilization is much higher. So again, a decent dual core processor such as a Core 2 Duo E8xxx or Phenom II X2 should be enough to get the most out of your graphics card in this game. While it is quad-core optimized, the game is not demanding enough on the CPU to warrant it based on what I have seen so far.