Hardcore DDR2 RAM by Corsair, G.Skill, OCZ and Patriot -
"DDR3 will reach higher clock speeds than DDR2, but it doesn't yet outperform high-end DDR2 modules. We look at some of the best high-grade DDR2 RAM available... From our experiences, we can clearly say that spending extra money on a faster processor will usually give you a better performance increase than devoting it to high-end memory... Each memory technology has a sweet spot, which is defined by the available memory densities. In case of DDR memory it was a total dual channel capacity of 2x 512 MB. DDR2 has its ideal capacity at 2x 1 GB, and DDR3 DIMMs will quickly move to 2x 2 GB next year..."
http://www.tomshardware.co.uk/2007/06/15/hardcore_ddr2_ram_by_corsair_uk/