You are better off selling the 7770 and just buying a 760 or something. Two low end cards in Crossfire/SLI is never a good idea. You'll get better performance and less headaches out of a single faster card.
I agree . Deffenitley try from GTX 660 OC Windforce 2GB GDDR5 awsome choice in 2 way sli ...which is enough and recommended for the BF4 so it will do.But the 7770 are not good deffenitley for sli