Sandy and Ivy have the same thermal profile. i.e. at the same wattage of power dissipated, they'll be at the same temperatures. Ivy, being more efficient on an architectural and structural level doesn't need the same amount of power to do the same work as Sandy. Hence, cooler. However
this doesn't take into account the fact that Ivy die is smaller than Sandy die, increasing the thermal density and making it harder to get the heat off it.
Haswell is hotter than Ivy using this same number (at same wattage, Haswell will be hotter). But it's probably canceled out by Haswell being more efficient than Ivy. Haswell then integrates the voltage regulator which dumps probably 10W under the IHS, thus making Haswell as a package hotter than Ivy.
Also, the FIVR is NOT the same thing as the Voltage Regulator
You realize FIVR stands for fully integrated voltage regulator right? It regulates 1.7V down to 1.2 or whatever the core voltage is, and does the regulation for the uncore.Edited by dr/owned - 6/9/13 at 2:32am