That is limiting the internet speed not the wireless..indirectly it does limit wireless users.
The setup is not done via interface it is done via ip or mac address. But you can match a IP and then limit it to 5m or you can get a group of ip and limit the group to 5m.
But you are back to the second part of my first post, find a router that you can load dd-wrt firmware on. The factory firmware is very limited in ability to limit traffic.