ati 7970 for mining

I have a Sapphire 7970 that I use for mining. The problem is that when I mine I usually only get 400-500kH/s sometimes less. i've been looking all the hardware comparison pages I look at though I should be getting about 600-800 kH/s more or less. My card has a stable overclock of 1100/1600. I am using cgminer 3.1.1. What could I do to get the higher hash rates with my card?

Would the version of cgminer affect it much?
Might bfgminer work better and if so what version?
Does catalyst driver version affect it very much?

i have been checking in other posts and this is what i found:
If you are using the GHz edition of the 7970 you're only going to get around 500-600 MH/s. There is something in the firmware that prevents it from using all the horsepower. If you have that card you need to flash the card with the regular 7970 drivers (from the standard cards) and then you'll get 730 MH/s.

but i think the cgminer does affect very much, which version can i use to get about 800?

thank you