Sadly Crysis 3 is a very demanding game; both CPU and GPU. The below benchmark is at 1280x800 high graphics detail and 2x anti-aliasing. The test rig uses an Intel Core i7-3770k @ 4.6HGz. A slower CPU will result in even lower FPS.
In comparison to the Radeon HD 7790, the Radeon HD 6670 DDR5 performance is only about 45% of the HD 7790. The HD 7790 gets 30 FPS, so 45% of that is 13 FPS and remember that is with a Core i7-3770k @ 4.GHz for a game that is known to be CPU dependent.
Hitman Absolution performance is also dependent on both CPU and GPU. But is not quite as demanding as Crysis 3. The below performance chart shows that a Radeon HD 7790 can get 49 FPS so 45% means about 22 FPS for the Radeon HD 6670 DDR5 GPU with an i7-3770k @ 4.6GHz.
Naturally, lowering the graphics quality and turning off AA will result in better performance.