They travel at the same speed, in the same medium. c is the speed of light in a vacuum, all EM radiation travels slower in any other medium. The complicating f

They travel at the same speed, in the same medium. c is the speed of light in a vacuum, all EM radiation travels slower in any other medium. The complicating factor here is that when you have electricity flowing in a wire, the fields are generally mostly outside the conductor, not in it. That is, the signal propagation delay depends more in what you are using as an insulator around wire than the material of the wire. This has had practical consequences in the past; if you replace the insulating jacket of one wire in a twisted pair with a slightly different material, on long runs it will ruin your signal.