1st: I have a powercolor Boost 7950 and there is a very small switch near to the crossfire connection that switches the bios to (non-boost) your sapphire card might also have a bios switch.

2nd: My card did do the same thing while mining at stock clocks try using one of the overclocking programs to change the clock, i use MSI afterburner and as soon as i change the engine clock it will then stay constantly there. My card can go over 1100mhz without changing the voltage but you could be conservative and change to 930mhz for example.

Hope this helps.