Cool'n'Quiet is AMD's program to alter system speed to reduce power consumption when the CPU is under its lowest load. This should be disabled before proceeding, since it's most likely incompatible with your manual overclock selections.
nForce 4 Ultra and nForce 570 SLI chipsets typically overclock beyond the capabilities of most AMD processors without raising chipset voltage, but increasing SPP, MCP, and HTT settings by 0.10V above stock might prove just the trick towards getting those last few MHz without causing heat problems. We'd try it only after first finding the maximum CPU speed at stock chipset voltage, though.
HyperTransport busses are fairly sensitive to clock changes. A good way to make sure that this vital link doesn't become a stability-limiting issue is to drop the HT multipliers to 4x when increasing HT clock speeds beyond 225 MHz, and 3x when the HT clock exceeds 250 MHz.
Dropping memory to the lowest speed setting is a great way to get the highest clock speed out of the CPU. For example, dropping DDR2-800 to 533 MHz data rate will allow a CPU overclock of 50% to bring the memory back up to its rated speed.
Using the voltages recommended in previous pages, the Sempron 2800+ should easily jump to 2.00 GHz at a 250 MHz HT clock, while the Athlon 64 X2 4200+ should just as easily go to 2.53 GHz at a 230 MHz HT clock. Stability testing should be followed by small increases in HT clock (around 4 MHz) and further testing until a point of instability is reached. Once you've exceeded the stability limit, lower the HT clocks in small steps (around 2 MHz) until the system is 100% stable.
Slower-than-stock timings increase RAM stability as it approaches its clock limit. The major rated latencies, tCAS-tRCP-tRP-tRAS, should be set to 5-5-5-15 while searching for the CPU's best clock speed.
Lower timings increase performance, and once the CPU's limit has been found, the lowest stable memory timings can be sought. The concept is to lower one latency setting by one cycle at a time, retesting until instability is found, and raise it back to the lowest setting where instability wasn't an issue. Repeat this procedure with each latency setting until the lowest combination is found. This type of testing often results in a locked system that requires clearing the BIOS, so make sure to record all BIOS changes before trying a change that might require starting over from the beginning.
Note that we've also been asked about advanced memory timings such as tRRD, tRC, tWR, tWTR, and tREF, but the majority of users will get the best results by leaving these in automatic configuration mode.