Memory performance
We'll begin by measuring the memory subsystem performance of these solutions—no minor thing, since there are such big differences between the system architectures. These synthetic tests won't track closely with real-world application performance, but are enlightening anyhow.

Notice that I've included a graphic above the benchmark results. That's a snapshot of the CPU utilization indicator in Windows Task Manager, which helps illustrate how much the application takes advantage of four CPU cores, when they're available. I've included these Task Manager graphics whenever possible throughout our results.

Sandra's synthetic memory bandwidth test is widely multithreaded, so it takes good advantage of all four of the Quad FX systems' memory channels and thus both halves of the NUMA memory subsystem. The result is realized throughput of nearly 15 GB/s. I should note here that, due to limitations in the Athlon 64's memory clocking scheme, the FX-74's memory modues are actually running at 750MHz rather than 800MHz—not that it hampers performance too terribly much.

Speaking of handicaps, the Core 2 Extreme QX6700 comes up a little behind the X6800, probably due to the fact that the QX6700's two chips each present a load on the system's front side bus, bringing with them additional overhead. That may be why the QX6700 is consistently, if slightly, behind the X6800 in memory bandwidth tests like this one.

The Quad FX system matches the Intel systems in memory access latency, falling a little behind the single-socket Athlon 64 FX-62. It's possible the FX-74 is hampered here somehow by NUMA overhead, but as you can see, CPU-Z's latency test is definitely single-threaded, so I'm not sure what to think. Regardless, all of these systems are very quick at transferring data to and from memory, the Athlon 64s mainly because of their integrated memory controllers and the Core 2 processors because of their sophisticated cache prefetch algorithms and the ability to move loads ahead of stores (a.k.a. "memory disambiguation").