In general, if a PC's motherboard is only specified for RAM up to a given core speed x, will that PC be faster with: RAM of latency y capable of running at a maximum core speed >x or RAM of latency <y capable of running at a maximum core speed of exactly x ? I would have thought the latter, but Crucial's Memory Adviser tool advises the former. So, which of us is correct - me, or the machine? (Here is a concrete example: I wish to upgrade a Toshiba Satellite Pro L300-155 laptop from its current 1GB RAM to 2GB Crucial RAM. The laptop's specifications are given here. I see from those specifications that the laptop is designed for DDR2-667 Ram. Crucial sells two compatible 2GB kits, priced exactly the same as each other: DDR2-667, CL=5; DDR2-800, CL=6. It seems to me that of these two upgrade kits, the first kit would run slightly faster on the L300-155 than the second, because both will presumably be capped at DDR2-667 core speed (see laptop specs), but the second kit has more latency. However, Crucial's Memory Advisor tool recommends the second kit.)