Intel 'Paxville' Xeon DP 2.8GHz
 

Less than 4GiB/sec to share between the better-performing four cores is pretty measly, with each Opteron core enjoying roughly twice that with interleaved accesses to a shared MC on 2-way dual-core Opteron. Downstream from the MCH, if you want to do any I/O, there's not much of a link to the ICH5R, itself really old, and only the PCI-X segment bridge gets any real bandwidth deserving of a high-end workstation system.

Link: http://www.hexus.net/content/item.php?item=4202