I recommend maybe overclocking the CPU side of the APU as well, I have an A8 laptop with discrete graphics in "dual graphics mode" (it's what they call hybrid crossfire with their APUs) and found the CPU was holding the GPU grunt back by quite a bit.
Also, what's your RAM speed?
ive set the cpu clock speed to 2200mhz using the built in amd vision control center. almost all the settings are set to full using the gaming preset, then i pushed the other settings up a notch to full.
ive now got 16ghz ddr3 ram, pc world checked what my original ram was and it was 12800 1333mhz so i bought another 2x 4g of them.
so now im all ram'd up im going to order the amd radion 6570 and use the crossfire thing to link them, ill probably post here if i have any problems!
would it still be possible to clock the discreet card as well and will the built in amd vision control center let me do that or am i better off using a 3rd party program??
thanks for all the help guys, its cleared a few things up, hopefully now i can start gettin the most from my pc