I've idly wondered about this and today I had a real world test.
I am copying a 64GB VM image between machines.
I knew it wouldn't work, but for fun I tried 802.11n. That was estimated to take days.
Then I tried Gb ethernet. OS X estimated 6 hours.
Then I tried firewire 400. It's little known, but 10.6 and earlier supported networking using Firewire (probably using Bonjour/Rendezvous discovery). Both machines assigned the one another an IP address and they connected (there was a little pizza spinning because I forgot to dismount a network share first).
The transfer was initially estimated to take 5 hours. Now it looks like it will complete in 30 minutes.
So it appears that OS X Firewire networking is much faster than Gb ethernet, which one wouldn't guess from the specs (Gb > 400 Mb). On the other hand, the firewire estimate started out as 5 hours and then suddenly sped up, so there's something quirky here.
Incidentally, doing firewire networking makes the laptop run hot. It's working ...