It's a half-duplex connection, with a scheme that resembles token-passing, and a kinda polling rate of 1000 times/sec. Add in command overhead and CRCs etc, and I'd expect a 480mb/s physical layer to yield perhaps 2/3 of that number in actual throughput for mass storage.

Which is just about exactly what it does. Cool.
On a commercial device that I wrote drivers for at both ends of the cable, we maxed out at about 35MBytes/sec.

Cheers
-ml