I have a setup using the A10-5800k and a 6670 DDR3. Without Dual-Graphics some games were ok, but sluggish at 1080 with some eye candy : Tomb Raider, Sleeping Dogs, Need for Speed Most Wanted. Often I would be sure to have the logo on the top of the screen to make sure that Dual Graphics is enabled.
Experience with Dual-Graphics is much better than either just the 7660D or just the 6670 DDR3. Ironically, my system's RAM is clocked higher than my video card's.