Here is the Cisco's answer for the question. What type of top speeds can you realistically get with 11n in the real world?

The answer is "it depends". The actual connection rate (at the physical layer) is dictated by the quality of the client's connection. This can be anywhere all the way up to 300 Mbps. Then, from that actual connection, your 'real' throughput is a bit lower. In a real world environment, the peak sustained throughput (per radio band) can be up to and well past the 100 Mbps mark. As with any wireless technology, mileage may vary based on myriad environmental and system variables. Look to 11n to provide a very significant throughput increase to existing 11a/b/g networks.