If you want to overclock, then you want the Core i5-2500K.
Non "K" CPUs do not have unlocked multipliers so the only way to overclock is to increase the frequency (the traditional way). However, the frequency is tied to everything so increasing the frequency too much can cause things like the USB ports to stop working or become damaged. 300MHz - 400MHz is probably the max overclock. The i5-2500K can reach 4.5GHz in most of the time, it varies for person to person.
with extra $20 (over your $200) you can get a core i5 2500k and oc it for extra speed. gta 4 loves quadcores. make sure you get a good after market cooler (e.g. coolermaster hyper 212 evo), a case with good airflow, a motherboard that supports overclocking (e.g. asus z68 v pro or gigabyte z68 ud3h b3 etc.) a good psu.
if you have microcenter access, you can get it even cheaper, $180: http://www.microcenter.com/single_product_results.phtml...
2300-2400 are all multiplier locked and only different in clockspeed. with higher clockspeed you get slightly higher fps.
Well this is what I recommend, go with an i3-2100 and a z68 mobo that says it has support for ivybridge. Then in 4 months use your saved money and money you have earned over the next 4 months for an i5-3570k.
I'm not sure I wanna half-upgrade right now. That i3 would be similar to what I have right now, and then I would spend more money on a CPU afterward.
Anyway, what is the main reason(s) why I would want to wait for Ivy Bridge? I read about them but, what does the data translate into?
Otoh, I don't usually prefer to wait because there's always something new around the corner month after month that I don't really bother unless there's a huge difference.
ivy bridge promises
10-15% cpu speed up over sb,
60% igpu speed up over sb,
slightly higher multiplier oc,
native ddr3 1600 ram support (i just read that ram oc might void your cpu warranty),
native pcie 3.0 support (twice the bandwidth of pcie 2.0),
native usb 3.0 support. thunderbolt (lightpeak) support optional.
lower tdp. configurable tdp in mobile cpus and in higher end desktop cpus. possible higher cpu overclok and lower power consumption compared to previous generations.
backwards compatibility with lga 1155 pch e.g. h6x, p67, z68 after a bios upgrade (on most mobos, you'll need to have a sb cpu present to perform the bios update).
these are untested though. however, motherboard manufacturers might have the cpus and might be testing with their products. reviews and benches won't be out until after april 9-ish (latest rumored launch date).
right now, sb is an available, mature platform. games don't take advantage of pcie 3.0...yet (and pcie 3.0 gfx cards are backwards compatible with pcie 2.0). usb 3.0 is available on all mobos with a 3rd party chipset. the only biggest diff. is pcie 3.0. other than that, ivb is similar to sb - it's just a cpu die shrink after all. next new arch will be haswell in 2013.