Don't forget that the PCI(e) GigE adapters are FULL-DUPLEX --> they can (in theory, and in practice under Linux) do the 700mb/sec or whatever in BOTH directions simultaneously.. giving between 1000mb/s and 2000mb/s total throughput capability.

Whereas USB2 adapters are stuck somewhere around 250-350mb/sec TOTAL.

Big difference there.

Cheers