best gpu for a8-6600k

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Hi everyone. I'm thinking about buying gpu for amd a8-6600k. I would like it be in crossfire with apu. (becouse i dont have much money). So i was looking and found out that 6870 and 6850 are better than 7750 wich i found crossfired with a8-6600k. So my question is: Is 6850 or 6870 will work in crossfire with this processor? Or maby you can suggest me another gpu around 100$.

 

[pospo]

i found someone said it will not crossfire with HD6870 only with low-end graphics cards. So 7750 is best choise?