This topic is 4 years old but deserves a bump! I recently had the time to bring back one of my old mining rigs which used 280X cards…
Yes this still works and yes I was able to undervolt to 0.950 and my rig of 4x MSI 280x 3GB cards is doing 2 MH/s total. each card is ~505 KH/s
using nsgMiner 0.9.3
Thank you @ghostlander