Ya 550MH/s is at at the stock clock speed of 925MHz. Sounds like CGMiner isn't clocking your cards up to the full 1125, because if it was, you should be getting closer to 650-675MH/s. Try using a 3rd party program like GPU-z to monitor the sensors tab, and see what the actual clock speed is.

One last thing is to add this line into your config. It will help with the power consumption and temps.