|metric relates to routing. It has nothing to do with priority of an interface.|
If I recall correctly the OS, when faced with multiple network interfaces, has an algorithm that tests thruput and chooses the fastest interface, which in your case will be the wired nic.
Only way I know of to do what you want is to do hardware profiles. In one profile you have the wireless enabled and the wired disabled. Just the opposite for the other profile.
Or just do what everyone does and manually disable the interface you are not going to use.