I have the option between an i7 2600k and a gtx 570, or an i5 2500k and a gtx 580? Which is better? I want to be future proof. I won't be able to upgrade my cpu for a year. I game, browse the web, listen to music, watch youtube etc.
I see lots of people suggesting get SLI GTX 560Ti's over a single GTX 580. 2 560's cost less, and perform better than a single 580. Might be something to consider.
A couple of 560 Ti's in SLI will surely perform better in most situations compared to a single 580. But there are advantages of getting a single card namely lesser driver issues, lesser heating, lesser power requirement and lesser noise. Thus the better option here is to go for a single 580 card.
I'd advise going with an OC i5-2500K if you are only concerned in playing videogames. From the benchmarks I've seen, it gives the best performance for some games, though the i7-2600K does come ahead occasionally. Where the i7-2600K trumps the i5-2500K is in video processing. If you plan to make, edit, and upload videos on your computer, definitely go with the i7-2600K. It shows a significant improvement over the i5-2500K in that area. But in reality, the main difference is price. In terms of framerates, you'll see maybe a 2-3 fps increase at most, but there are rare exceptions like Fallout 3 where the i7-2600K pulls between 6-10 fps more than the i5-2500K.
I have also heard that the i5 is nothing more than an overclocked i3. How true this is, I don't know, so you'll want to double-check me on that. But from what I've seen, you can OC an I7 much higher than you can an i5. An OC i7-2600K @5.0ghz will outperform an OC i5-2500K @4.5ghz.
If you plan to majorly overclock your system, I'd advise going with a 3rd party site like Origin. The reason is if you overclock your processor, you immediately void your warranty. However, these 3rd party sites will warranty your OC system, meaning if their effort was too ambitious, you're not out $300.
As for the GPU, go with tri 580s in SLI. Tri 580s in SLI outperform anything out on the market right now.