to be honest, im using a pentium g620 and i'm completely satisfied in games (currently playing swtor a bit). hardly notice a difference between that, and my friends i5-2400 that i built a few months back. i'd save your money, maybe grab and SSD if u dont already have one.
I'm currently rocking an i3-2100 and HD6850 and am thinking of bumpin up the CPU to the new ivy bridge 3450 to have a quad-core CPU. Will many games benefit from this? Such as GTA 4?
I know many games will run the exact same, which is a bummer, but even games that will love a 4 core CPU, will there be much gain with this HD6850 in terms of FPS?
The i-2100 will not bottleneck the HD6850. In fact it will not bottleneck even CF of the GPU.
But If you can afford it now, it is good to get the 3450. It got good gaming performance + the other benefit of being a true quadcore & ivy bridge (less power, PCIe 3 support). etc.
The 3450 is recommended as best processor for the money at its price range of $200 http://www.tomshardware.com/reviews/gaming-cpu-review-o...
But take note that the i5-2500K which is higher clocked & unlocked is just $20 away. But is does not have native PCIe support. But that doesn't matter in today's GPU.