USB 2 operarates at 480mbits per second as long as both devices are USB 2 and any cabling is USB2 spec. Firewire is 400mbits ps and 800mbits ps, again as long as all items used correspond.

A tip if using USB, try and use the ports built on the mobo as these will be USB 2 spec, some cases only use USB1 ports through the front.

You can buy an external gigabit network HD enclosure as long as the PC you use has this port: gigabit Lan port 1000mbit per second though this is expensive.