Memory Upgrade Question

[Chaz Master]

I am upgrading my memory and i dont know which one would give me the best performance:
1.Corsair 2GB DDR XMS3500LL Pro TwinX (2x1GB) CAS2 (MY-093-CS)
2.Corsair 2GB DDR XMS4000PT TwinX (2x1GB) CAS3 (MY-094-CS)

Thanks