The thing is that having four double-sided DIMM modules in an Athlon 64 based platform requires the use of 2T Command Rate setting, which has a negative effect on the performance in this case.
Moreover, there is one more disadvantage of having four DIMM modules in your system, which is indirectly related to the topic of our today’s discussion. The use of four memory modules in Athlon 64 platforms reduces significantly the overclocking potential of the platform by limiting the bus frequency increase. For example, a lot of Socket 939 mainboards refuse to raise the clock generator frequency over 240-250MHz when they are equipped with a full set of four memory DIMMs. By simply removing a pair of DIMMs from the system you can immediately raise the stability bar beyond 300MHz.