There is no way to prioritize the wifi traffic itself. In many cases it is interference from a neighbor using their wifi. It is impossible to control someone elses usage.
This is the major problem with wifi everyone tries to use the same limited bandwidth and everyone just stomps on each other.
Not sure using different nic cards means you should have loaded different drivers. Many times strange issues are related to driver problems but it would be unlikely on 2. Be very sure you are using the drivers from the card manufacture or chipset vendor and not the generic ones in windows.
Other things you can check are that you do not have any form of power saving features turned on. There is also some autoconfig option the...