Do you save any Wattage by underclocking like this?
I have my 7950 Twin Frozr iii overclocked to give me 620Kh/s but I have also undervolted it to 1100mV to reduce the power draw.  I reckon that I might be able to drop the volts a bit more but havent bothered to check yet.  These cards are built to overclock so it doesnt really bother me that much to keep the settings high, especially if you can reduce the voltage at the same time for an all round benefit.