http://www.tomshardware.com/reviews/...mark,3120.html
Not untill games start using more cores.
Games prefer more powerfull cores over multiple cores.
Your CPU would be right on par with a pentium g630, so You should be fine with your current one for gaming untill at least haswell.
http://www.anandtech.com/bench/Product/55?vs=406
a quad wont give you that much of a boost in gaming, the IPC and clock of the new chips will. Just overclock what you have.
http://www.anandtech.com/bench/Product/55?vs=288
GPU like a 6850 might be a better investment, but two 4850s is still a massive force to be reckoned with. What resolution are you playing at?