iXBT Labs posted a review on the Intel Core 2 with Various FSB/Memory Clock Rates.

For our tests we'll take motherboards with two top chipsets: Intel X48 and NVIDIA nForce 790i Ultra SLI. Both of them support top Core 2 configurations: sterling support for PCI Express 2.0, all DDR3 memory standards (at least for memory modules with SPD -- EPP 2.0 or XMP), 400(1600) MHz FSB. The question now arises of how relevant the latter property is for common users, considering that only one processor with 1600MHz FSB has been launched so far? Answer: it's not relevant, of course. But tests of this mode will help us get a better idea of what is going on. Besides, this mode can be considered as an isolated case of overclocking, so we can estimate which memory should be used to overclock a processor.

Let's take a look at absolute values of performance gain. In 7-Zip, the fastest configuration with Intel X48 (DDR2-1066@5-5-5-16-2T) accelerates the system with ) 1066MHz FSB by 6.5% versus DDR2-667@4-4-4-12-2T. Not bad: the difference corresponds to CPU multiplier 0.5. That is other things being equal, this performance gain makes the same difference as a one-step-faster CPU. This effect amounts to +8.3% in Doom 3. Here is the main conclusion for this group of tests: contrary to purely theoretical assumptions, faster memory accelerates the system up to DDR2/DDR3-1066. Is it a coincidence that the maximum effective memory frequency matches the FSB frequency? We'll try to find an answer in the next parts of this article.