Someone that overclocks could answer this better but I wouldn't be concerned. RAM speeds periodically encounter manufacturing hurdles that don't match the capabilities of other components. Intel seems to compensate for the mismatch very well. Changing a processor of 1066 FSB with a newer 1333 FSB CPU hasn't affected me so far with 800 MHz RAM. Presumably mismatches are dealt with using virtual memory (hard disk) so performance would suffer when multitasking or using demanding applications. Newer applications that can use, or have features that require, the newer CPU instruction sets are another issue. That means that a perfect computer with the proper amount and speed of RAM will always be outdated by any newer software you require.
I'm upgrading my x38 chipset boxes to core 2 quad. That leaves the processors that were there, both 1333 MHz FSB. The boxes I want to move them into are Q965 chipset. One of the procs is an E6750. Q965 will support an E6700 (1033 FSB). Memory is 800MHz. While I don't expect the overall speed to be the same, if it works at all, it'll be a big plus (over a 3.4GHz Pentium D). The only question is: will it work?