What should I upgrade?

alright you guys I have a question to ask which component should I upgrade? I currently have an amd fx-4100 cpu and a gtx 550ti gpu. I am a gamer and I do video editing,rendering and encoding. I would like to know what I should upgrade. I have around 300 dollars to spend and it will be quite awhile until I can upgrade again. If I were to upgrade the cpu I would get a new mobo and intel i5 ivybridge or if i get a gpu I am going to buy a gtx 660ti. I want to know which will make the biggest difference for me and if my current cpu is going to bottleneck the gtx 660ti.