Hi,

Memory modules faster (333, 400,...) than 266 MHz can run at this speed (compatibility).
The mostly advantage is 400 MHz or 333 MHz modules are really no more expensive that the same 266 MHz. Then, later you will be able to upgrade (by a new motherboard) without change memory modules too.

Anyway, I don't know if the differents CL speed of modules modify the Peg II performances and if it can be change (CL parameters).

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Blaster