Memory throughput when writing: only at high clock speeds can DDR2 memory better the throughput of the old DDR1.
When writing, things are even worse: here the performance of CPUs with lower clock speeds really falls apart. With a 2 GHz processor (Athlon 64 X2 3200+) the memory bandwidth is a whopping 200 MHz/sec below the DDR1 value, achieving a paltry 5.6 GB/sec. Only at high clock speeds - 2.4 GHz and above - does performance rise above the values of the old DDR1 memory.
The strong dependence of DDR2 memory on CPU speed represents a huge performance loss for midrange processors when compared against DDR1 versions. This is also reflected in the performance of practical applications.