Intel’s Pentium 4 architecture was one of the most bandwidth hungry - if you shoved DDR into it with a 400MHz rate with extremely low latencies, the system would perform worse then if it had 433MHz memory with higher latencies. Pentium 4 was just so memory hungry that higher MHz was better than lower latencies.

[NLN=Intel Conroe Memory Settings Guide]http://www.tweaktown.com/articles/947/[/NLN]