@AternosHUN
Hi,
For MediaTek Wi-Fi modules the Registry method should work well.
To do that open regedit, go to HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Class\{4d36e972-e325-11ce-bfc1-08002be10318} , click through all the "00xx" keys until you have found the one belonging to your Wi-Fi card. Once there create a new "String Value" named NetworkAddress and fill it with your desired MAC address (like AABBCCDDEEFF). After that open the Device Manager and "Disable" the Wi-Fi card and then "Enable" it again. Now check if the MAC address of the Wi-Fi card has changed or not.
If you google it you should be able to find dedicated software on the Internet that can also do the above.
Data throughput over Wi-Fi depends heavily on the quality of the signal. Without knowing the environment in which the Wi-Fi card is used (like distance to router, walls, channel congestion) there is no way to tell if 40 Mbps is reasonable or not.