I'm just reporting what I've done and seen. This isn't something I've read, something someone else said, or a lopsided unequal test on a stacked deck.
Both external drives are based off of 2.5" drives. Different manufacturers. 320GB firewire vs 500GB USB 2.0. Same sized Intel MacBook image. Same file copied to both drives from the same server. Same version of NetBoot/NetRestore off a Mac OS 10.5 partition on each drive.
Takes about a half hour on the USB and 45 minutes on the firewire.
Could be a Mac driver thing. Could be that there's a hardware glitch with the 320 drive. Could be a lot of things.
But now look at how many desktops, servers, and laptops have USB 2.0 vs. 1394 ports... The market speaks for itself.
Firewire has been full-duplex since 800.
320GB firewire vs 500GB USB 2.0.
There's the problem. The larger hard drive has more density or more platters, which are factors in how fast they can write data. File write speeds vary by over 300% on different hard drives. It is easy to get a 2.5" hard drive that can't consume Firewire's bandwidth.
But now look at how many desktops, servers, and laptops have USB 2.0 vs. 1394 ports... The market speaks for itself.
Back to my assertion of market vs. technical superiority. One of the reasons for ubiquitous USB is simply market force. Companies put it on computers (BTW, Apple was the first to drop legacy ports for USB) for all their low-speed stuff, so people started expecting it to run everything.
Another problem was cost. Apple and the other stakeholders wanted a per-seat royalty plus the parts cost a couple dollars. It was cheaper to use USB and live with the speed hit. As most people wouldn't get to try Firewire, they really wouldn't know the difference.