Generally speaking, higher MHz RAM is better due to the faster rate of transfers, but that is only one side of the story. There is a clear point of diminishing returns in RAM speed as well, so it does not make sense to spend a lot of money for minor increments in performance beyond a certain point. Moreover, you also have to take into account the CAS Latency (CL) of the memory modules, which acts as sort of a counterweight to RAM speed. Higher CAS Latency is detrimental to the module’s performance even if the MHz rating is high.