So your target temp is 75, but what is your actual temp? Because you have your argument for your clock to be 0-1125, so it could be that CG is clocking down your card in order to get it to run at a cooler temp and hit your target. Just thinking out loud, dont know for sure.
I have two 7970 in an antec 900 case (closed, 5 fans running 100%) and these things are 86c and 97c.
That's with stock settings no overclocking. Yes, they run about 550Mhash each per the spec.
Guess I need to open the box and blast them with a fan or plunge into water cooling...