to be completely honest here, your bottleneck isn't going to be coming from either your ram or cpu (unless your running some crazy ass predict the weather typer deal) its going to be your harddrive. Memory has gotten to the point that it really doesn't matte especially with speeds from ddr3.
Ultimately the speed of the RAM vs Hard rive will be sufficient however the amount of ram required can pose a problem for cost, namely most racks have limited provided slots for ram and often use a combination of larger/smaller cards. However a cheaper option that Iím yet to see mentioned is tri or dual channel memory a.k.a 4 x1gb 1600mhz or 6x1gb 1600mhz.
Though as hardware isnít my department Iím not sure if 2u or 1u racks have motherboards in support of this due to the size though if so it could both provide a significant increase in speed and degrease in the cost of replacements compared to for example 4x 1gb 1600mhz vs a single 4gb 1600mhz and as such provide twice or three times the read/write capacity.