I don't notice the micro stuttering you guys are talking about with my A8-5600k with 6670 combo, but I did hook up my HDMI to the 6670 rather than the motherboard. AMD says to hook up the display to the faster card, whether that's the IGP or dedicated card.
On my retail box, it says both the A8 and A10 can go in dual graphics mode with the 6570 and 6670. The A6 can DG with the 6450(?) and 6570. Obviously, the APUs will have their optimized DG cards.