actually, Firewire will give you better performance.
FireWire, uses a "Peer-to-Peer" architecture in which the peripherals are intelligent and can negotiate bus conflicts to determine which device can best control a data transfer
Now, USB 2.0 uses a Master/Slave architecture in which the computer handles all decision functions and dictates data flow to, from and between the attached peripherals (adding additional system overhead and resulting in slower data flow control) .
And actually if you find a device that has 1394(b)...another version of firewire...it can support up to 800Mbps. Now in terms of hard drives, I've always just stuck with internal ones. Mainly 'cause these have even MORE throughput than firewire or USB. However, external ones are nice if you don't have room inside the computer, need it to be portable, or just want to look cool. However, if your friend is saying to get a firewire card and an external drive it's probably because he wants you to get a dedicated audio hard drive so you're not recording on the system drive....and recommending firewire so it's just plug and play.