Newer games are likely coded in a way that suits scalar GPUs. You would therefore see a proportionally lower utilization on the more rigid, wonkier VLIW-era products, and thus lower performance as well.
what surprises me is the variation from one game to the other, considering they are all targeting the same hardware
Max Max which is based on the same engine from the Just Cause game
http://pclab.pl/art65638-10.html
behind the 260X not by much, while on Just Cause 3 it's under half.
similar results for the newest Assassins Creed I posted earlier
Metal Gear 5,
http://pclab.pl/art65645-10.html
clearly ahead of the 260x
while Wticher 3 on low settings (looking at Miasto City)
May 2015
260X 30-34.2 (min-avg)
6970 27-32.1
http://pclab.pl/art63116-7.html
October 2015
260x 29-35.1
6970 18-21.6
http://pclab.pl/art66374-5.html
seems like the same test scene and settings, looking at the 260X also the same performance, but the 6970 dropped performance badly with the latest updates and drivers!?