I have a 7970 Double D edition from XFX... The Double -D's were built to overclock like its no one's buisness.
I am sure that you would be able to max your 7950 DD out in CCC and see framerates that would make you feel like you have a stock 7970 in your system. Imo, a better value dollar per dollar then a stock 7870.
Good luck with whichever way you choose to go!