Which one should i get

[blobeb]

I've already got the A6-3500 should i get the 6670 and Xfire them or should i get the 6850 and use it alone?

 

[Sunius]

HD6850. If you xfired 6670s, you'd run into micro stuttering and other problems tied to lower-end multi gpu setups.

 

[refillable]

Well if you put a 6850, the GPU part on the a6 will be disabled, and the CPU part will only work, which is pretty bad...