Conclusions
We've covered a lot of ground here. There are plenty of differences between the chipsets' feature sets, and in some cases, we saw surprisingly divergent performances in our application and peripheral benchmarks. Let's break things down chipset by chipset.

ATI Radeon Xpress 200/ULi M1573 — This is one of the more intriguing chipsets because it features chips from two different companies. Generally, the pair is competitive, although there's definitely something wrong with the ULi south bridge's NCQ implementation, at least as far as IOMeter is concerned. USB performance isn't too hot, either. That's really a shame, since the M1573 is the only south bridge in this round-up to support the Intel's High Definition Audio standard. But don't forget the Radeon Xpress 200's trump card: its DirectX 9-class integrated graphics controller. If integrated graphics is your bag, the Xpress 200 has no peers in the Athlon 64 world, and SurroundView is pretty sweet for multimonitor fans.

NVIDIA nForce4 Ultra — The nForce4 Ultra is probably the most common Athlon 64 PCI-E chipset on the market, and it certainly offers more features than its competitors. It's the only chipset to support Serial ATA II and ATA RAID, and it appears to be the only one with command queuing that works. The NCQ implementation could be improved, though, as evidenced by the superior performance of Intel's NCQ-capable south bridge chips. ActiveArmor Gigabit Ethernet acceleration can also apparently be improved, although with one of the highest throughputs and easily the lowest CPU utilization, the nForce4 Ultra's GigE controller looks pretty sweet as is. However, NVIDIA's bundled firewall software has lost some of its luster since Microsoft included a much-improved firewall in Windows XP Service Pack 2.

SiS SiS756 — SiS's chipset is the latest to offer PCI Express support for the Athlon 64, and for the most part, it looks to have been worth the wait. The SiS756 takes the crown in WorldBench, and it's one of only two chipsets with an integrated Gigabit Ethernet controller. An apparent performance bottleneck in IOMeter is cause for some concern, though. SiS likes to talk about how its chipsets are optimized for streaming media, and I can't help but wonder if those optimizations may impede the storage controller's ability to handle multiple outstanding I/Os. The SiS965's lack of command queuing support probably doesn't help matters, either.

VIA K8T890 — In many respects, the K8T890 is the elder statesman of Athlon 64 chipsets with PCI Express. It was the first PCI-E chipset to be announced for the Athlon 64, and it's still using a dated VT8237 south bridge. Performance is decent, though, with the chipset putting on a particularly impressive show in our USB tests. Still, it's hard to get excited about a chipset that lacks NCQ support and is almost exclusively implemented with only two Serial ATA ports. If it were paired with VIA's new VT8251 south bridge, which purportedly will feature Serial ATA II support, High Definition Audio, and four-port Serial ATA RAID, the K8T890 would be much more compelling.

So which Athlon 64 chipset reigns supreme? That's a tough question. The K8T890 does not; that much is certain. With the exception of USB, its performance is nothing special, and you'd need something special to get over the VT8237's relatively weak feature set.

SiS's entry looks very promising, but the IOMeter performance wall is worrying. Also, given recent history, it seems doubtful motherboard manufacturers will use the SiS756 for anything but low-end products that generally don't offer the extra goodies that enthusiasts have come to expect on a motherboard. It's hard to get too excited about a chipset that may only be found on boards from ASRock, ECS, and Foxconn. Those boards may well be solid budget choices given the SiS756's performance in our tests. Still, I wish DFI, Abit, or one of the big three would take a stab at building an enthusiast-oriented motherboard based on this chipset.

So we're left with the Radeon Xpress 200/M1573, which is a clear winner for integrated graphics platforms, and the nForce4 Ultra, which is well-rounded enough to take on just about anything else. If you don't need its IGP, the Radeon Xpress 200/M1573 combo's poor USB and command queuing performance are going to be disappointing. The nForce4 Ultra, on the other hand, is a much better all-around performer. It may lack support for high defintion audio, but it's got just about everything else, including our Editor's Choice award.