To overclock today we used Catalyst Control Center, other software we tried exhibited a little instability with the new hardware.
We managed to push the core by 10.5% before instability would occur – hitting 1,054mhz. The GDDR5 memory could be pushed to 1,490mhz before artifacting was noticeable (5960mhz effective).
Pushing the card to the limits helped increase performance past the level of the default clocked XFX R9 280X.