Conclusions
AMD has consistently touted its model of continuous improvement for chip fabrication techniques, and that model has served it well in the recent past. The products of a well-refined 90nm process have more or less held their own on power efficiency against 65nm processors from Intel, except for at the very high end. Chips produced with AMD's special low-power 90nm process tweaks, like the Energy Efficient 3800+ and 4600+ we tested, have been especially impressive. The flip side of that coin is that AMD's move from 90nm to 65nm does not instantly produce huge improvements in energy efficiency or clock frequency headroom. Instead, the 65nm transition brings a welcome but incremental improvement in power consumption over current Athlon 64 X2 products and little or no additional headroom. If you're looking to buy an Athlon 64 X2, then I'd definitely try to grab the 65nm version, but don't expect miracles from it.

AMD will no doubt continue its trajectory of gradual improvement to its process tech, leading to additional power savings and headroom at 65nm in the future. For now, though, making it over this hurdle isn't nearly enough to overcome the sizeable performance gap between the Core 2 Duo and Athlon 64 X2—and it does very little to counter the formidable presence of Intel's quad-core Core 2 Extreme QX6700, which is coming in lower-power, lower-cost Core 2 Quad form soon.

That said, AMD could make one considerable stride toward countering Intel's quad-core chips and salvaging its poorly received Quad FX platform by replacing the Athlon 64 FX-70-series processors—and their scorching 125W TDP ratings—with chips made on this 65nm process. A pair of FX-74 CPUs, each with a 65W TDP, would be the perfect answer to Intel's Core 2 Extreme QX6700 and its 130W TDP. Pair 'em up with a decent, affordable motherboard, and Quad FX might start grabbing some attention—for the right reasons. Note to AMD: You need to do this. Stat.