I tested it with my router (NETGEAR WNDR 3700 Gigabit/Dual Band N router (A/B/G/N). the NIC only tested at 100Mbps. It is not a Gigabit NIC at all. What also does not make sense is that the WIFI card is not dual band. It only works on th b/G/N (2.4ghz) band. The 5.8 ghz A/N band is much more suitable for media so this is big time mistake on Micro$oft's part.
The add on card they sell for the old 360 is A/B/G/N compatible, go figure what the &@$% they were thinking with the built in wifi card and NIC on the XBOX 360 S.