Just in case you missed this article, THG has released a study on the impact of memory speed and timings on computer performance:
Tight Timings vs High Clock Frequencies
If you just want the bottom line, then here it is:
"we would not advise anyone to spend a lot of money on highest end memory in the hope of improving computer performance by increasing memory speed. ... as long as you have enough memory - preferably 2 GB - the extra money you pay for more memory speed would be better invested in a faster graphics card"
Tight Timings vs High Clock Frequencies
If you just want the bottom line, then here it is:
"we would not advise anyone to spend a lot of money on highest end memory in the hope of improving computer performance by increasing memory speed. ... as long as you have enough memory - preferably 2 GB - the extra money you pay for more memory speed would be better invested in a faster graphics card"