Dual GPU Devil 13 HD 7990 comes with a turbo switch that overclocks the GPU from 925MHz to 1000MHz. The switch doesn’t affect memory, which will remain at 1375MHz (5500MHz GDDR5 effectively).
Note that the memory is specified at 1500MHz and we had no trouble upping the clock from 1375MHz to this number. The GPU cooperated quite well too, and we easily overclocked it to 1125MHz without any voltage or fan RPM changes.
PowerColor has its own overclocking tool dubbed the Powerup Tuner, which offers basic options to overclock the GPU, memory or manage fan RPM.