Is the speedtest is good for checking your radio's performance/bandwidth ???????

The wireless medium is half duplex.Remember that radio is only responsible for capacity or performance of your wireless link.Online speed contains multiple TCP ACKs and NACKs.Which slows down the speed as it consumes more bandwidth.Moreover your are not actually measuring your wireless speed.Because your TCP session is between your test PC and speedtest server.So in this case the connections from PC-->Switch-->Slave/SM--->Master/AP--->ISP switch--->ISP cloud--->somewhere speed test server are involved.So basically I want to say that you are actually testing your complete path capacity.
The recommended speed test tool would be use IPERF or JPERF test tools.
1.Install IPERF on PC-A and PC-B.
2.Connect PC-A directly below the Master / AP radio.
3.Connect PC-B directly below Slave / SM radio.
4.Run multiple TCP / UDP streams from PC-A all the way to PC-B.
5.Check speed results.