Karadjgne :
What I wanna know is why it seems we have been lied to all these years about so much. I mean really, all these gpus packed to the gills with massive bandwidths, high clocked memory, huge amounts of cuda etc, and thenalong comes Maxwell with 1/2 of this, 1/4 of that, sucks up only 63w, doesn't even need external power and is almost as good as its bigger brother the gtx760. And now we get reliable OC of 4.4 on anantiquated 'H' mobo, when everyone knows you can't OC without a 'Z' board? WTH! I'm starting to feel like a sheep that has had the wool in my eyes for years.
Basic answer: newer architecture.
First, the 750 is completely different architecture than the 760. And performance-wise, it's more than a step behind the 760. However, the idea behind it is not unlike going from the P4 to the Pentium M and Core architecture: efficiency and elegance opposed to more power and brute strength. I think you'll see this trend continue in GPUs, and I welcome it.
The H81 board isn't exactly "antiquated" considering it's only the previous generation. And I think it's safe to say the H81 is a lot more capable than the old H61 boards. Also keep in mind that Haswell has VRM on the chip itself, so power management is less about the mboard than it used to. Finally, the G3258 is roughly half the TDP of the i7-2600K. You simply don't need as much power to run it, so you don't need 12+ phases like you used to.
As for requiring a Z board to OC, that's a software restriction, not a hardware one. It seems mboard manufacturers had an agreement with Intel that the "lesser" boards wouldn't expose the clock multipliers. There was no hardware reason the older chipsets couldn't OC, they were simply restricted from doing so through firmware.
So really, the only place we were "lied to" was about the boards. The older chipsets would have OC'd just fine had they not been locked down. And this has happened many times in the past. It's just like the old nForce boards that could unlock Athlon XPs.