DDR2-800 represents a 50% clock speed increase when compared to DDR2-533, which is reflected in the power requirements we measured. The test system required 148-189 W power with two DDR2-533 DIMMs, and adding two DIMMs meant an 8 W increase. According to the tests we did in part one of the power saving guide, we would expect an increase of approximately 4 W when upgrading from DDR2-533 to DDR2-800. Indeed, the power requirements at DDR2-800 dual channel now are between 151 and 193 W, which is very much the ~4 W we predicted.
All of this happened at default timings of CL5-5-5-15. As we increased the timings to the ideal setting of CL3-4-3-9 at DDR2-800 speed, we also had to increase the memory voltage from 1.8 V to 2.0 V. This had a measurable impact on the power requirements of up to 2 W. Again, 2 W is of little relevance to desktop PCs, so it makes sense to go after the memory with the quicker timings if the cost difference is acceptable.