Ninjalane has just posted their review of the mid-range performance memory from Mushkin, the HP2-6400

Knowing that size plays a deciding factor in performance what separates one module from another? In a word, speed. Every module is assigned a speed rating from the manufacture that is largely dependent on the quality of the chips but can also be affected by module (PCB) design, the voltage requirements, and settings required to maintain a given level of performance. This roughly translates into frequency and latency.

Mushkin HP2-6400 4GB Memory Review