My Sapphire factory OC 7950 at stock clock 950/1,250 makes around 500Mh/s. If I turn the clock up to 1,050 it makes around 600Mh/s, but the fan goes 100%. Also, in case you didn't realise, for mining Bc your memory clock is not a big factor - according to my wall power monitor, if I still run 950Mhz, but turn my memory clock down to 800, the card uses about 200W vs 220W at stock memory clock. Interestingly, it also hashes slightly higher - at around 520Mh/s!

FYI I run an A10-5800APU and use my onboard video as well - and it contributes an extra 100Mh/s @ 800Mhz!