Core 2 Extreme: 3.66 GHz And FSB 1333
The tuned-up Core 2 Extreme ran with an FSB clock rate of 333 MHz, which translates into 1333 QDR. The standard specification calls for 266 MHz (1066 QDR).
To enable drastic increases in memory performance for the Core 2, we raised the clock rate for our DDR2 modules from 400 MHz up to 555 MHz. This increased memory throughput substantially, from 5.8 GB/s up to 7.3 GB/s - nearly 26 percent.
The screenshots that follow show the various motherboard settings that allowed us to deliver that kind of performance. Specifically, it was absolutely critical to increase memory input voltage from 1.8 V to 2.15 V. You needn’t worry about damage occurring as a result, because modern production processes ensure that the memory stays cool and remains stable. The setting labeled "DDR2 - 889 MHz" appears in the BIOS for the Asus P5B Deluxe for a memory speed multiplier of 3.33. Thus, an FSB clock speed of 333 MHz produces a memory clock rate of 555 MHz (QDR 1110). We also increased the CPU input voltage from a stock 1.3 V to 1.48 V, or roughly 12.1 percent. This proved quite workable, even using the CPU cooler included with the processor in its retail package.
These BIOS settings let us run the CPU at 3.68 GHz, with a memory clock rate of DDR2-1110 (555 MHz).
The Corsair memory modules worked well with timing values of CL4-4-4-8, even at 555 MHz.