Just slightly off topic but what settings - if i may ask - are you using for the Sapphire 7950s? The one in my rig is running at an avg of 603 kh/s, getting it to 630 would be nice. Currently I am using cgminer with

shaders = 1792
intensity = 20
engine = 1075
memory = 1500
w = 256
thread-concurrency = 25088
lookup-gap = 2
threads = 1
auto-fan

and nothing else. I experimented for a day or two with all sorts of settings but this was the fastest I could come up with. Have I missed something or is it just my card? The model I am using is

http://www.newegg.com/Product/Product.aspx?Item=N82E16814202026

EDIT

Just found a tip somewhere else on the forums here - enabling powetune +20 effectively turns it off and stops the cards from trying to save power. it increased my hashrate from 603 kh/s to an avg of around 635 kh/s - thanks roy7 for that tip.