Why are 7950s better than 7970s? From all my research, a 7950 is created when the cpu and other parts of a 7970 have flaws in manufacturing, so the gpu maker just disables that part and calls it a 7950 instead, with the needed BIOS changes.
But what is it about 7970s that make them worse at mining? I have a 7970 that has been pushed to 665 Khash in mining LTC, but the temperature was touching 90C. I have 3 HIS Ice-Q 7950s that hum along nicely at 630 Khash and 75-80C, and they could probably be pushed to the same 665 or very nearly so if I tried.
Even though my 7970 touched 665, it is usually running around 500-600 by having the intensity cut back, because I don't want to leave the A/C running all day to cool the room off. It gets hot if I don't.
1) You should undervolt your gpu before it burns.
2) Try and get a better setting for your HD 7970 as you should be getting 700-800 overclocked.
3) HD 7950 is better in term of hash/energy.
