We generally start our CPU and chipset testing with memory benchmarks, and they can be useful, but in this case, I would caution you that the Radeon Xpress 200 doesn't have a memory controller. That's on the CPU. Instead, most of the performance differences you see between the Radeon Xpress 200 and the VIA K8T800 Pro in these tests are likely the result of slightly different internal timings in the motherboard BIOS or perhaps just some variances within the margin of error of our tests.
The one place where memory bandwidth does matter is in the case of the Radeon Xpress 200 when its integrated graphics core is in use (noted on our graphs as "Radeon Xpress 200 IGP"). Using system RAM for graphics memory will steal some bandwidth from the CPU, and our tests show how much.
The Radeon Xpress 200 doesn't really give up much memory bandwidth with the IGP enabled. Interleaved access to the local frame buffer probably helps a bit on this front.
Memory access latencies are only slightly higher with the IGP in use, and they're still way, way lower than the Pentium 4 with the 915G chipset.