Let's start by talking about the Athlon 64 X2 4200+. This CPU generally offers better performance than its direct competitor from Intel, the Pentium D 840. Most notably, the X2 4200+ doesn't share the Pentium D's relatively weak performance in single-threaded tasks like our 3D gaming benchmarks. The Athlon 64 X2 4200+ also consumes less power, at the system level, than the Pentium D 840just a little bit at idle (even without Cool'n'Quiet) but over 100W under load. That's a very potent combo, all told.
In fact, the X2 4200+ frequently outperforms the Pentium Extreme Edition 840, which costs nearly twice as much. Thanks to its dual-core config, the X2 4200+ also embarrasses some expensive single-core processors, like the Athlon 64 FX-55 and the Pentium 4 Extreme Edition 3.73GHz. Personally, I don't think there's any reason to pay any more for a CPU than the $531 that AMD will be asking for the Athlon 64 X2 4200+.
If you must pay more for some reason, the Athlon 64 X2 4800+ will give you the best all-around performance we've ever seen from a "single" CPU. The X2 4800+ beats out the Pentium Extreme Edition 840 virtually across the board, even in tests that use four threads to take best advantage of the Extreme Edition 840's Hyper-Threading capabilities. The difference becomes even more pronounced in single-threaded applications, including games, where the Pentium XE 840 is near the bottom of the pack and the X2 4800+ is constantly near the top. The X2 4800+ also consumes considerably less power, both at idle and under load.
The X2 4800+ gives up 200MHz to its fastest single-core competitor, the Athlon 64 FX-55, but gains most of the performance back in single-threaded apps thanks to AMD's latest round of core enhancements, included in the X2 chips. The X2 4800+ also matches the Opteron 152 in many cases thanks to Socket 939's faster memory subsystem. Remarkably, our test system consumes the same amount of power under load with an X2 4800+ in its socket as it does with an Athlon 64 FX-55, even though the X2 is running two rendering threads and doing nearly twice the work. Amazing.
There's not much to complain about here, but that won't stop me from trying. I would like to see AMD extend the X2 line down two more notches by offering a couple of Athlon 64 X2 variants at 2GHz clock speeds and lower prices. I realize that by asking for this, I may sound like a bit of a freeloader or something, but heyIntel's doing it. No, the performance picture for Intel's dual-core chips isn't quite so rosy, but the lower-end Pentium D models will make the sometimes-substantial benefits of dual-core CPU technology more widely accessible. If AMD doesn't follow suit, lots of folks will be forced to choose between one fast AMD core or two relatively slower Intel cores. I'm not so sure I won't end up recommending the latter more often than the former.
Beyond that, the giant question looming over the Athlon 64 X2 is about availability, as in, "When can I get one?" Let's hope the answer is sooner rather than later, because these things are sweet.