802.11g runs at up to 54MbpsNot in the real world. 15 mbps would be a reasonable expectation for a fairly optimal setup, and I'm sure that less than 10 is not uncommon.
I don't have a feel yet for typical 802.11n performance, but given that the theoretical maximums that were advertised for a, b, and g were all essentially fictional, I'd be surprised if the same didn't apply there.
Best regards,
-- Al