Any bus that can support a 1000 bits? (or 125MB) The PCI bus technically can but isn't used anymore. Due to overhead it really can't. And as soon as something else is plugged in it really can't. I believe most have a single PCIe lane attached to it, which is 250MBs large.
PCI is 32 bits @ 33 MHz = 1,056 Megabits per second, raw bandwidth
PCI-E x1 is 2,500 Megabits per second / 10 = 250 MB/second
So, both have enough raw bandwidth to support GbE (Gigabit Ethernet).
The comment above is correct: the old PCI bus is shared
across all devices that use it, whereas PCI-Express does
not suffer from that limitation.
We run Intel's PCI GbE adapters in several workstations,
and they are very fast: you have to factor in the
firmware and hardware efficiency of the adapter itself,
particularly when 2 of the same Intel GbE adapters
are communicating directly with each other.
Cross-vendor GbE tends to slow down, in our experience.