I see many people still can`t decide what memory to choose for their C2D rigs and what performance should they expect from desired kit. XbitLabs made pretty good review on almost all memory combinations. Article is very usefull for both high-end users and those on a budget cos it has tests from 533@5-5-5 to 1067@3-3-3. As we know NV 650i chipset allows practicly independable memory clocking and the boards are cheap. So if you`re questioning to pick DDR533 or DDR667 but still be able to OC your E6300/E6400 to it`s full potential, but don`t know what performance hit you might be experiencing compared to DDR800/DDR1067 - this article is for you

Pleasent reading

Choosing the Right Memory for Core 2 Duo Platform - Part 1
Choosing the Right Memory for Core 2 Duo Platform - Part 2
Choosing the Right Memory for Core 2 Duo Platform - Part 3

Same article in russian - all graphs combined