Simply skip to BIG QUESTION if you're in a hurry
90% of reviews focus on P67/Z68 boards and the I5 2500K / I7 2600K. The rest is usually about mATX boards and I3 2100 or Pentium CPUs. Actually, I've only found a single (as in "1", read "one") CPU review - click - that would discuss in some useful details the I5 non-K CPUs from the perspective of limited OC - by means of the 4 bins (+400 MHz) and Turbo Boost (+100 to +300 MHz). The review platform included a P67 board, obviously. Still, kudos to Xbit Labs guys for bringing this up.
Also, Xbit Labs are the only site that have done a thorough review of an H67 board with a non-K I5 CPU - click - explaining how a non-K CPU can actually be OCed, in a limited manner, naturally. Again, kudos are in order.
So, we now know that any I5 / i7 SB CPU can be overclocked by at least 500 MHz (for all 4 cores) on a P67/Z68 board - courtesy of the "limited unlocked" multiplier (4 bins, for a total of +400 MHz) and Turbo Boost (+100 MHz, and lets leave it at that, we only care for 4 cores loaded simultaneously). This is supported by these reviews and by several people on various forums, my humble self included - I've a P67 board and I5 2400 running happily at 3.6 GHz.
Now, things get more complicated - enter H67. If you followed the second link, to the 2 x GB mobo review on Xbit Labs, you probably read that with I5 2400 the H67 board did not offer the 4 extra bins for all cores, but only the Turbo feature. The reviewers claim that the options for changing the multiplier are grayed out in the last screen (for the H67 board) - but this is only true for Turbo (which still works anyway, so no big deal). However, the screen clearly shows that the multiplier is in white, which means it can be accessed and played with. It shows x31, which is the def max speed for I5 2400 w/o Turbo. What we don't know is whether the multiplier can be also raised or only lowered.
Follow me still?
Now, my brother recently upgraded his work PC to a GB H67 mATX board and I5 2500K, along with some hi-endish SSD and stuff. A weird combo, but he says he followed the advice of the PC store guy where he buys his PC stuff. Wish he consulted his older geek brother. Anyway, he calls me and says "Hey, I got this new PC cause I really need speed now and I know the CPU is great for overclocking and all." So I tell him that he actually won't do much with it because the H67 board has no overclocking features. Anyway, after I briefed him on the manner of OC on 1155 and unlocked multipliers and all, I told him to go to BIOS and see what's in there. He says: "Hey, the main multiplier, the one on the top of the screen, goes up!" Says I: "Bleeep the bleeeping bleeep!?" And he goes on: "Believe me, it goes up from x34 to x37". Which is exactly 400 MHz, the 4 bins - as in P67 and I5 2400. So I told him to pump it all the way up and leave it there at x37. That way he gets some OC at least. He also says the Turbo works OK and takes the CPU to x38 under Prime95.
Still here?
OK, so we now know another thing - that a H67 and I5 2500K can actually use the +500 MHz trick.
The BIG QUESTION is - can you owners of H61 and H67 boards with I5 2300, 2400 and 2500 non-K CPUs confirm that a limited OC of 500 MHz is also possible for such setups?
If you own a setup like this, please take a minute to go to your BIOS and report back on what you can do with the main multiplier (x29, x31, x33 depending on the CPU).