What's the fastest connection speed / shortest elapsed time using Migration Assistant?

Gigabit ethernet to gigabit ethernet. Next would be FireWire 800 to FireWire 800. Thunderbolt target disk mode is testing to be equivalent to FireWire 800 in target disk mode.

It looks like the OS can keep a gigabit link fuller than target disk mode is able, even when the target mode link has vastly higher bandwidth available.

While the prevailing thinking that gigabit is faster than FW800 is true in the most rudimentary theory it doesn't hold up in practice. When migrating over Ethernet the source machine has the OS loaded, and is communicating over a chatty protocol designed for the wild unknown that is an open network.

Firewire transfers with migration assistant are performed with the source machine in "target disk" mode... no OS is loaded, and it's essentially functioning as an external hard drive.

In my experience FW800 in target disk mode provides superior performance.

I just transferred a 25GB user from a MacBook Pro 5,3 running 10.7.5 to a MacBook Pro 9,2 via Gigabit Ethernet (direct cable connection with self assigned IP addresses). It took 23 minutes although the time-remaining indicator going from 5 to 8 then dropping to zero for most of that time.

I then transferred that same user from the MacBook Pro 9,2 in target disk mode to a MacBook Air 4,2 running 10.7.5 via a Thunderbolt and it took only 5 minutes with the time-remaining indicator dropping monotonically from 3 to 0.

I conclude that Thunderbolt is much faster than Gigabit Ethernet.