Spar916 :
Hi everyone. I currently have an i3-3220 installed in my PC. It's not a bad CPU but I'd like something a bit faster with more cores. I'm thinking about buying either an i5-2500k or an i5-3570. I'm not sure which one of these I should get, as a friend of mine said that the difference wouldn't be big since I could just overlock the 2500k. Price difference isn't huge but I'd prefer to save the money.
The 2500k is Sandy Bridge. The 3570 is Ivy Bridge. There is practically no performance difference between these two generations. Ivy Bridge is just Sandy Bridge shrunk down from 32nm lithography to 22nm. So the biggest differences are Ivy Bridge uses less power (95W TDP vs 77W TDP for the two CPUs you've listed), and it has a better integrated GPU (which was completely redesigned). Since you're using a discrete GPU, the integrated GPU is irrelevant. There are a smattering of small things they changed as well (e.g. better random number generator).
So it pretty much boils down to price and your system's power consumption. If you can get the i5-2xxx or i7-2xxx for significantly cheaper than the i5 or i7 -3xxx, and your'e ok with the extra power consumption and heat it'll generate, then just get the Sandy Bridge. (Be careful to compare turbo clock speed, not base clock speed. Ivy Bridge's lower power consumption gave it more room to turbo boost. So the i5-2500k with a base 3.3 GHz would turbo by 100, 200, 300, 400 MHz on 4, 3, 2, or 1 core. But the i5-3570 with a base 3.4 Ghz would turbo to 200, 300, 400, 400 MHz on 4, 3, 2, or 1 core. So on multiple cores the 3570 actually has about a 6% clock speed advantage, not 3% as its base clock speed implies. The i5-3470 is actually more comparable to the i5-2500k.)
*** Please note that if you use the computer a lot (say, 4-8 hrs/day), the cost of the extra electricity you burn with Sandy Bridge can easily add up to $10-$40 over 3-5 years. So the more expensive Ivy Bridge may be cheaper in the long run. ***
As for i5 vs i7, the hyperthreading in the i7 makes a significant difference only in a video rendering, data compression, and a handful of games. So unless the price difference is very small, I wouldn't bother with an i7. Save the money for your next complete system upgrade. One caveat is that in these generations, Intel only gave the i5 6MB of L3 cache, while it gave the i7 8MB of L3 cache. So even with hyperthreading disabled, the i7 will slightly outperform an i5 at the same clock speed. So you should probably add about 5%-10% to the i7's clock speed to account for this when comparing prices.