Memory Speed and Triple vs Dual Channel Tested on Core i7
 

In general, the Core i7-based machine turned out to be even less sensitive to RAM than that based on Phenom II X4. The average performance drop caused by the transition from DDR2-800 to DDR2-400 was 11% on the AMD platform. Today, Intel's platform demonstrated the even lesser sensitivity of only 8%.


The performance difference between the dual and triple-channel modes is far greater. Sometimes, enabling the 3rd channel can boost performance by another 10%, though such cases are rare. On average, the worst you can expect from using Core i7 in the dual-channel mode is a 6% performance drop.

http://ixbtlabs.com/articles3/cpu/ar...2009-7-p1.html