Graphics card overclocking?
Try OCCT or Furmark. Both have error checking. GDDR5 memory has error checking and correction ,so your overclock may appear stable but will actually slow the card down if it is producing errors..
OCCT
http://www.ocbase.com/
Furmark
http://downloads.guru3d.com/FurMark-1.8.2-download-2523.html