Bandwidth, latency, Pifast, Lame
Kicking it off with a look at bandwidth and latency.
There shouldn't be too much to choose between chipsets designed for Athlon 64 CPUs for the simple reason that optimisations, usually carried out via a tweaked memory controller, aren't possible here.
Latency is also predictably fantastic. Note that the XPRESS 200's scores are the result of running a discrete GeForce 6800 GT 256MB PCIe graphics card. Bandwidth and latency would be a touch higher if run with the IGP in non-embedded mode.
ATI's chipset shows considerable performance promise by turning in the fastest Athlon 3800-based time we've seen thus far. The difference between it and a VIA K8T800 Pro board is negligible. Both AMD setups spank Intel's 3.8GHz 570J just where it hurts.
There's literally no performance difference in Realstorm's Raytracing benchmark.