What exactly driver need for HD7970 (R9 280)?
http://www.guru3d.com/files-categories/videocards-ati-catalyst-vista-win-7.html
On AMD Catalyst 14.6 RC2 (14.200.1004.0 June 20) driver two HD7970 get me only 0.50 chains/day.
On Crimson 15.12 driver three HD7970 get me 17 chains/day.