I have an HP ENVY dv6 laptop that came dual graphics enabled with the 7640g 512mb and 7670m 1gb. I'm just wondering if I would get better gaming performance out of just the single 7670m, or if I enabled the dual graphics and had the 7640g and 7670m working together.
Using dual graphics should yield higher framefrates.
That being said, the dual graphics is crossfire and you might run into problems with micro stuttering. Also, you might be limited to 512 mb of VRAM because of the 7640g. Also also, the VRAM might be slower with the 7640g because it is shared with the system RAM (not the case with the 7670M which has its own DDR3 memory.)
Give it a shot playing a game with each setting. The best way to find out which is better is to test it.
Edit: I guess I should attempt to answer your question. I would personally try to run the 7670M alone. Never been a fan of AMD dual graphics.