Hi,I know this thread is kind of old. I hit the wall with default voltage (1.25V) on the matrix 280x at about 1110 mhz. At 1150, it wanted 1.30V to keep it stable. The interesting part is, I can turn the voltage down at 1110 to min allowed 1.188 and ...

The ability to set fan to 10% as its the minimum for asus r280x matrix in the ati control panel. The gpu tweak will allow only as high as 20%.