Or buying the K version is just an overkill?
I have an i5-3570 (non K). Stock performance is just fine (with a decent GFX card of course). On a Z77 board, you're not limited to stock perf though and can hit a potential max 4.2GHz. Non-K i5's Ivy's aren't "locked" like i3's, they're "limited OC". You're still looking at +800MHz over stock (max Turbo + 4-bins) though:-
i5-3570 normal Turbo = 3.8GHz 1-2T / 3.7GHz 3T / 3.6GHz 4T
+ 400MHz limited OC on a Z77 board of Sandy & Ivy Bridge's (though not Haswell's) = max Turbo of 4.2GHz 1-2T / 4.1GHz 3T / 4.0GHz 4T.
If your motherboard has "Multicore Enhancement", it could potentially have a max OC of 4.2GHz under all loads.
I've done just that with mine, and never felt the need for a K chip for 4.4GHz, etc, it's just so fast even at 3.8-4.0GHz. Technically if you added 2.5-5% BCLK, you could reach 4.3-4.4GHz - best to just aim for a stable 4.2GHz though keeping BCLK @ 100Mhz. All you need to do is literally set your multiplier to 42x, enable MCE & Turbo Boost and that's it. Most can hit 4.2GHz stock voltage. Likewise, an i5-3470 can hit 4.0GHz, and an i5-3350P can hit 3.7GHz the same way, for even bigger bargains.
