What does say the slide below, if you dont understand what is mentioned then i wonder why you are even trying to talk about CPUs...What data?
Where does it show that Intel chips are undervolted?
At the same site from where the slide originate, with 7% undervolting all you could do was to run Windows but certainly not Prime or IBT, same at Hardware.fr where they didnt even bother to do their usual undervolting test, i guess that it will be the same that the previous gen, that is MBs "unexpectedly overvolting" the CPUs...
40% wouldn't even put it close to Broadwell either if you compare with Excavator.
It depend what you are comparing, in Integer based code it s more than enough while in FP, as pointed by their rendering demo, it s apparently, and logically, significantly more than 40%.