A good WiFi card/adapter is only as good as the signal interference in the environment will let it exist.
Take my home as an example, not to large. Footprint of about 50' x 100' feet 2 floors. I need 3 access points for decent coverage of WiFi... Why? My house is metal framed & we have 220 aC running across part of it. This make the house a virtual Faraday Cage. (look it up)
What I'm getting at is the Adapter, be is USB or PCIe is only as good as the clean and clear radio signal it can SEND AND RECEIVE, to and from the Router/AP.
So, if you have a desktop tower with antenna on the back side, directly attached to the card/case, they are liely being hampered by all the rest of the computers electrical signals. Hence my addition to which ever you get, the extension antenna's.
Rant off