If you are running a DDR2 capable motherboard which does not support increasing memory voltage or only by a little bit, you must get this memory. Even at the stock voltage of 1.8 V it overclocks like mad, from the advertised DDR2-525 all the way up to DDR2-743.

No matter which CPU and cooling you have, you will always be able to run this memory in sync with your FSB (max. 371.5 MHz, x14, which is the lowest multiplier a current P4 can run, you end up with 5199 MHz). Unfortunately the overclock does not scale with voltage, but the budget-aware overclocker will not need a higher memory clock anyways.

Latencies can be tightened some. Depending on how much you reduce them, the maximum clock will be reduced as well. Finding the optimimum tradeoff between latency and clock frequency requires experimentation on the users side.
What makes this memory even more attractive is the price: about $120 for the 1GB kit with such overclocking potential is really good.