DirectX 11 class graphics card performance
The mother of all resolutions, well the most popular one. Here we are at the most common used resolution for the Radeon/GeForce gaming class, 1920x1080/1200 are the most preferred monitor resolutions this year and age.
Even though the GeForce GTX 660 is sufficient I'd say a 660 Ti is the better yet more expensive choice. AMD Radeon wise well, the cards are performing okay overall. The Radeon HD 7870 will be suitable.
And last but not least the mac-daddy of single monitor resolutions, on a 30" 2560x1600 pixels monitor, this resolution will require a spicy graphics card as it renders over 4 Mpixels per rendered frame (!). Here on AMDs side the Radeon HD 7900 series manage decent here, but the GTX 680 takes a small lead. But with these image quality settings both brands are running out of juice fast though.