Well, it depends a lot on what your doing. My opinion on it though is that faster ram is better. For example, I am running my system at a lower speed just so I can get a faster FSB and faster ram clock (149mhz cas2). Anyway though, it also depends on how much of a MHz jump your wanting to take on the CPU, ex: I would rather replace a 500mhz cpu w/ a 1ghz cpu then pc100 ram w/ pc133.