just for your reference, i'll share my story, while the only difference being i'm using ASUS DC2 HD7970 TOP (factory OCed 1000) but that was before the officially GHz edition were released.
In the end i had to RMA them 4 times to get them right.
it was a cross fire setup
so the first RMA was sweet and easy, the replacement card that came back was PERFECT! in every way, not like the POS that came in the box from the store
but the nightmare began with the 2nd card in RMA, I had to do it 3 times to finally get a good card
like you the original cards, or actually all the bad cards will crash into those horizontal or vertical lines in 3Dmark or any heavy 3D games.
the problem behind the heat caused by the OC and the cooling not being properly mounted, or not properly done to the VRAM
there's also this thing with the NEW BIOS firmware being better optimized and properly volt-ed/clocked without getting generating additional heat
i noticed the OLD BIOS were underpowered which probably made them unstable, and there was the HSF issue with the DC2 not being properly mounted
the NEW BIOS from the new replacement cards were clocked and volt-ed adequately, and the HSF was actually doing the job it was supposed to be doing, and seems like they added HS as well over the VRAM, while before the VRAM were naked, and were just cooled by air without HS
so, the final decision is yours. if you want to risk another RMA or not
if it doesn't crash on 99% of your games and maxed out settings on 3Dmarks11 or Vantage then you should be fine
Choppiness is usually caused by something else, try 12.7 beta drivers instead
do a full swipe or clean uninstall of the old drivers first
do NOT use 12.8 drivers they are bugged to hell, even Firefox crashes on 12.8