I agree with mocchan, Phenom x4 is still very capable.
Altough, I kinda disagree about the i3 statement. Yes they perform very well on games, because games dont use so many cores, and i3 has 4 really efficient cores.
However, for about the same price of a i3-21xx you can get an FX8120, which, for starters, is unlocked and competes as very well with it in gaming performance. Besides, it gives you 8 cores instead of 4 (data taken from anandtech itself, same site you mocchan referred to)
You probably have an AM3+ mobo, so an FX should fit nice in your machine, and it does not bottlenecks that graphics card at all.
So, thats my take on the issue. The FX option, in my humble opinion gives you an overall more customizable CPU, better overclocking, you can turn off a core per module making it a 4-core is you need it to and bumping up the performance to match a 2500k in lightly threaded apps, etc. The other thing is that Win8 introduces changes to the threading management for AMD chips, so quite a big bump of free performance might come from it.
So thats it, the Phenom will be up to the battle, so dont feel that you must upgrade right now.
Cheers!