In theory the speeds are:
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12 Mbps-Universal Serial Bus (USB)
400 Mbps-FireWire (IEEE 1394A)
480 Mbps-USB 2.0
800 Mbps-FireWire 800 (IEEE 1394B)
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Personally I would go for a USB 2.0 external hard drive,because most computers don't support Firewire 800.