@johnkeates:
@VAMike:
legacy pci slots are half duplex and bandwidth limited for gigabit traffic. you should be able to get more than 200Mbit, but there may be some limitations in the pci bridge. at any rate, pcie is a much better option.
Looks like we're seeing this PCI limitation more and more often ;-) Maybe we should put this in the Wiki.
Definitely for dual port cards, they really needed the PCI-X extensions (higher clock speed + 64 bits), which have been functionally obsolete for over a decade and aren't found on any current mobos AFAIK. (If there's a PCI slot at all, it's probably a bridge to PCIe, possibly shared with some other legacy stuff, and not really intended for high-bandwidth applications–it's just there for people who have some old serial port or firewire card or somesuch they don't want to get rid of or pay to replace with a new PCIe version.)