DDR2 vs. DDR: Revenge Gained
 

DDR2 memory tests, which we have performed earlier, showed that its higher latency is exactly the reason why it gets defeated by the regular DDR SDRAM. However, now the situation is changing. The leading memory manufacturers offer DDR2 modules with improved timings, which make DDR2 look completely different from what it used to be.

http://www.xbitlabs.com/articles/mem.../ddr2-ddr.html