Sapphire r9 280x Vapor-x
Was unable to undervolt in afterburner but trixx and VBE7 worked great.
Now stable in my BAMT rig @ 750kh/s, 1080/1500, 1075mV
About a 70w drop in power draw per card

EDIT: exact version of the gpu is R9 280X Vapor-x 11221-02-40G