The RX480 killing mobos really isn't much of an issue for miners since we all use powered risers. The ribbon risers usually have a thick 16AWG cable connected to the molex, I am sure this cable can handle 100Watts no problem.
However no idea how those USB risers will work since they are powered by the SATA connector and those usually have a smaller gauge cable then regular molex.
The Risers I have coming in have a molex on the board and come with a SATA - molex connector. I'm just going to plug the molex right into the riser.