i have attached a screen shot on a Bandwidth Test.
it is between a AP Bridge <-----> Station Bridge.
on AP Bridge the average Tx = 19.3Mbps and Rx = 18.3Mbps
whereas the link speed on the Station Bridge is shown as Tx = 52.0Mbps and Rx = 58.5Mbps
now my question … why is this difference in speeds?
In the wireless registration that is the speed it is connected at not the actual transfer rate.
dont worry about it
thanks 
that is the difference between throughput and the actual connectivity. Like your LAN card is 10 or 100 or 1000 mbps and connects at the same to your respective switch but data transfer differs depending on cable quality, card quality and switch quality or other network conditions.