I'm looking at purchasing another pair of external hard drives to archive my image files. I'm seeing some good deals on USB 2.0 drives. As a mac user, I'm wondering if I really would detect much of an improvement in file transfer speed using a usb 2.0 vs Firewire 400? Before I make a purchase I would like to hear from other mac users. The bottom line is I don't want to pay too much for storage. However, my entire image collection is stored on external drives that I must access frequently.