guyz is it 7970 vapourX or a MSi gtx 680 oc edition??
Probably should point out what your friend, not yourself is running. How many monitor's is he using? How high of a resolution? What is he using it for?
Please read the thread of responses you've been given. The answer, is NEITHER.
Only one had half-vouched for the GTX680 since they recomended a 7970 as well while there are far more people vouching for the 7970, so that is out.
One post cited concerns about cooling issues with the VRAM, so that's a STRIKE ONE! on your pick of a 7970
One post cited it's a waste of money for a 6GB card except at serious gaming with 3 monitors in eyefinity, unless you post more details on your friends usage, thats a STRIKE TWO!
Every post in favor of the 7970 made a 3GB recomendation AND a different brand/model of the 7970 so STRIKE 3!
Both of your choices struck out. If you insist on helping your friend, give up on insisting people make a choice on your two preferences when they feel bothered enough to make every recommendation but your choices.