The 7950 Black DD is a great card BUT look at the differences:
XFX 7950 Black DD: 5500MHz GDDR5, GPU 900MHz, 1792 Cores.
XFX 7970 Ghx DD Edition: 6000MHz GDDR5, GPU 1050MHz, 2048 Cores.
So yes, OBV the 7970 is better even if you wont buy the Ghz Edition.
Enjoy