That's probably not going to work out well... Trying to crossfire two cards of different capabilities tends to cause all kinds of super-annoying problems that don't affect single GPU systems.
If you need more crunch power in graphics, then get a 7000 series card and just use that. If you don't, then keep the system as it is. If it's not broke, don't fix it. 
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Do not meddle in the affairs of archers, for they are subtle and quick to anger.
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Troll Hunter
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