If you mean best performance for that CPU without creating a noticeable bottleneck then the GTX 960 is probably the best choice.
If your budget is $250 the best performer is the R9 285 with a 550w-600w PSU.
If your budget is $230 then its between the R9 270X and GTX 760 with a 550w PSU.
If your budget is less than $200 the Nvidia 750ti and R9 260X with a 450w-500w PSU.
If you can't afford either of those cards keep an eye out for cheap Nvida 650 ti boost cards. They perform similarly to the 750ti and can often be cheaper. Good luck!
If you mean best performance for that CPU without creating a noticeable bottleneck then the GTX 960 is probably the best choice.
If your budget is $250 the best performer is the R9 285 with a 550w-600w PSU.
If your budget is $230 then its between the R9 270X and GTX 760 with a 550w PSU.
If your budget is less than $200 the Nvidia 750ti and R9 260X with a 450w-500w PSU.
If you can't afford either of those cards keep an eye out for cheap Nvida 650 ti boost cards. They perform similarly to the 750ti and can often be cheaper. Good luck!