Why native device support from chipset is better
For KT133, KT266, KT333, KT400, and some old Nforce2 motherboards, many devices are supported by the PCI bus. PCI bus has max bandwidth of only 132 MB/s (32 bit x 33 MHz).
Due to the use of legacy motherboards, many high speed devices such as IEEE 1394 (firewire) devices (HD, optical drives, video devices, camcorder, ...) are still running on firewire ports supported by PCI bus.
IEEE 1394 is a high speed serial bus standard that supports data transfer rates of up to 400 Mb/s (in 1394a) and 800 Mb/s (in 1394b). A single 1394 port can connect up to 63 external devices. As such, a firewire port is reaching the PCI bus limit. If there are more than one firewire port and more firewire devices are used, the PCI bandwidth and PCI bus contention would limit the performance of the connected firewire devices.
The 250 GB (compared to non-GB) chipset allows less device dependence on the PCI bus, whose bandwidth is way imbalance compared to an A64 system bandwidth (max_HT_BW to max_PCI_BW = 60:1), until PCI-express becomes main stream.
PCI-express 1X, 40 pins, maxBW = 2.5 Gb/s (basic link)
PCI-express 16X, 168 pins, maxBW = 5 GB/s
PCI-express and devices (post 17)