I've done another test

I ran DRI_PRIME=1 glxgears, just to keep the card running

I then launched BioShock and the sclk & mclk again stayed at their lowest
settings, I echo'd high into power_dpm_force_performance_level which changed
the sclk & mclk values. When I echo'd auto back into
power_dpm_force_performance_level and the clocks stayed high. When I exited the
game (with glxgears still running) the clocks went back to their lowest
settings, which is what I'd expect

So it looks like then the card is re-initialized the auto performance level
doesn't work correctly - or is being set to low

Hope this helps