S!
Both nVidia 6xx and AMD 79xx series will run CoD sufficiently. Which is better is up to the gamer to decide
I am happy with my 7970HD as it runs every game I play (WoT, EVE, IL-2 CoD, Arma2 and it's mod DayZ, Iron Front etc.) with great performance. And I bet nVidia 6xx series will do that as well
Interesting to see what the 12.8 drivers for AMD will do, being released this week..