OCIA.net takes a look at the Corsair 2GB XMS PC4000-PT Dual Channel DDR Kit in their latest review.

In order to find the maximum stable overclock, I first set the HT multiplier to 3x and increased the CPU voltage to 1.7v (to factor out the processor as a limiting factor). I used the maximum multiplier for my CPU, which happens to be 9x. Starting at 250 MHz 1:1 and worked my way up from there, increasing memory voltage as needed.

Corsair 2GB XMS PC4000-PT Dual Channel DDR Kit Review