Nice article from: http://networking.ringofsaturn.com/PC/pciexpress.php
Bandwidth
PCI Express in all it’s flavors: 1x, 2x, 4x, 8x, 16x and 32x all have much greater bandwidth than basic PCI.
Common Buses and their Max Bandwidth
PCI 132 MB/s
AGP 8X 2,100 MB/s
PCI Express 1x 250 [500]* MB/s
PCI Express 2x 500 [1000]* MB/s
PCI Express 4x 1000 [2000]* MB/s
PCI Express 8x 2000 [4000]* MB/s
PCI Express 16x 4000 [8000]* MB/s
PCI Express 32x 8000 [16000]* MB/s
IDE (ATA100) 100 MB/s
IDE (ATA133) 133 MB/s
SATA 150 MB/s
Gigabit Ethernet 125 MB/s
IEEE1394B [Firewire] 100 MB/s
