umm.... a 6570 would be a better match and the scaling with that kind of crossfire doesn't work too great. I would just pick up a 7750 for ~$50 with rebates, and then you can double your fps, without facing cfire issues.
http://www.newegg.com/Product/Product.aspx?Item=N82E16814131481&nm_mc=AFC-C8Junction&cm_mmc=AFC-C8Junction-_-na-_-na-_-na&cm_sp=&AID=10446076&PID=3938566&SID=