Up first are some simple memory performance tests. These results won't tell us about real-world performance, but they do have an impact on that.
The X2 3800+ is the only Athlon 64 among the bunch, dual-core or single, that runs at 2GHz. As a result, its bandwidth scores are a little bit lower than the rest, but they're still quite good. With dual channels of DDR400 memory and a built-in memory controller, the X2 3800+ has a very fast memory subsystem.
Linpack shows us, among other things, the basic performance of the cache hierarchies on these CPUs. A second CPU core is no help in this single-threaded test, and the X2 3800+ is again the lowest-clocked Athlon 64 in the group. You can see, also, how its performance drops off once Linpack starts crunching on matrix sizes above about 576K. That's where we hit the limits of either core's 64K L1 data cache combined with its 512K L2 cache. The Athlon 64 processors with 1MB of L2 cache perform better with larger data matrices, as does the Pentium D, which packs a 1MB L2 cache per core.
When it comes time to grab data from main memory, the X2 3800+ is very quick. That's the big advantage of its integrated memory controller.