Originally Posted by REAVER
How many sticks of RAM do you have? If you are using 2 identical sticks then they will function in dual channel mode, effectively doubling their speed. As long as the speed of your RAM is equal to or greater than the FSD you'll see no differance in speed.
When running in dual-channel mode, the actual throughput increase is not anywhere close to double on the current Core/Core 2 architecture. There is a small increase in available bandwidth when using dual-channel mode. The difference is really neglible in every case except when running the Intel GMA950 graphics card, as that will show more of a benefit because it uses system RAM as video RAM.
Having the FSB and RAM frequencies match is similar to the difference between 533 and 667, which is just about zero. On the current Core/Core 2 platform, the CPU doesn't take a performance hit when running with 533 RAM instead of 667. Matching the two for best performance used to be true with the Athlon XP platform, as that CPU took a large performance hit when running FSB/RAM at a-sync. With today's platforms it's either not an issue, or there's a very small difference.
Ghaz, there really isn't a difference between the two speeds, as the extra MHz of the 667 is all but cancelled out by the lower latencies of the 533. Sometimes the 533 is a bit cheaper than 667, sometimes not; but you really can't go wrong with either one.
Hope this helps!