My C0 used 1.375V VCore and 1.26V QPI to get 4.2GHz stable, and my D0 does it at 1.24V VCore and 1.36V QPI. What changed? Nothing really. The heat output is the same. I was excited for a bit about it but now I'm rather non-plussed. I was lucky with both of these chips as I have seen worse.
Yes I have noticed this too... At the beginning, I was wondering if this could be just a big scam... like the same chips, but it SEEMS that it needs less voltage but in reality, 1.24V D0 = 1.375 C0 or something...
Everyone knows that all chips are different, but it is still noticeable that D0 GENERALLY seem to have an easier time getting to 4ghz on lower voltages... but D0s are sometimes overhyped indeed...
D0s can be worse than C0s, not all chips are the same.. No chips are EVER guaranteed something else than stock... Just that on average, some chips have either a good or bad chance of getting a lower voltage higher OCs etc... D0 aren't usually much, or any cooler than C0s... But more D0s use less voltages and get higher OCs than C0s... You can't deny that the D0 is still an improvement over the C0, but it is hard to say how much of an improvement it is.
You still have a good chance of getting a pretty good chip no matter what though... I mean, with a D0, I probably am sure most chips can do 4ghz on air without going say over 85 load... (Estimating a aoltage though is hard to do) Perhaps not all, but your chances are still high...
Whatever I just said can be completely false though, since I have seen very few OCs, and the i7s I did OC were quick OCs... Never Oced one more than 1ghz over stock...