We used Corsair XMS2 DIMMs that are rated for CL3-4-3-9 operation, but the quickest timings we could select were CL3-5-6-9. Setting other cycles in the BIOS would not result in anything faster.
Most 975X motherboards are fairly overclockable, and can be driven at speeds 50% faster than specified. We used an MSI 975X Platinum Powerup Edition, which we managed to run reliably at up to FSB1600 speeds. This is an excellent result, which was only surpassed by the nForce 680i SLI motherboard.
This motherboard worked fairly smoothly. The BIOS recovery feature is pretty nice, as it allows you to reactivate the former BIOS state after a failed overclocking attempt. The memory dividers aren’t as good, as they are referred to as static memory speeds, but these will change as you alter the system clock speed. So you have to calculate the appropriate memory divider which fits your chosen FSB yourself : at FSB1066 speed and DDR2-800 memory, the bus-to-memory ratio is 266 MHz bus to 400 MHz memory, or 2:3. If the system clock is increased to 300 MHz, the memory will be overclocked proportionally. If this would exceed your DIMMs’ maximum clock speed, you will have to step down to another memory divider, such as the DDR2-667 setting. A plain text clock speed would be very helpful here.
FSB1600 (400 MHz base clock) was the fastest stable speed we could reach. You might be able to squeeze out a bit more if you are willing to invest the time. We reduced the multiplier to 7.0x to make sure that the CPU would not become a bottleneck for overclocking.