As I understand it, C2D systems generally show benefits from faster RAM speeds up to about 1.25:1. Beyond, it's usually just the synthetics that benefit. Not really sure, but I'd imagine that Quad processors might not mind even faster speeds, maybe up to 1:1.5?
__________________ i7 2600K | ASUS Maximus IV GENE-Z | GTX Titan | Corsair DDR3-2133
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