you might need to upgrade your ram before getting a new gpu. Most modern games require 8gb ram so I suggest getting 4-8gb extra totaling 10-14 gb which should be enough for now. (8gb ram cost about 30$/€)
Your cpu should be able to handle anything up to a gtx 980 without causing any major bottlenecks. Other than that you're good to go.
I can't really suggest any new gpu since I don't know your budget. Which psu do you have?
Ps. you might want to wait another month untill after pascal's release. Current gen gpus will be much cheaper by then.