Tom's Hardware Guide tests out what's best to get most performance out of your memory modules: high clock frequencies or tight timings?
From a memory requirement standpoint, a pair of 1 GB memory modules is undoubtedly the best choice for a high end computer today. The main purpose of a comfortable RAM size is to offer sufficient memory for your applications, and to prevent Windows from swapping application data to the swap file on your (relatively slow) hard drive. In this context, neither the memory type nor the speed is as important as simply having enough. The only thing we recommend in terms of memory size is to use two modules, to allow you to run in high performance dual channel mode.