i say all intel board has vdroop especially Asus boards, so if u set 1.55v in bios, ur prolyl geting 1.52v in windows and 1.5v full load (i had GA-965-DS3 and P5W DH they have same droop)
badaxe is prolly the least vdroop boards(exclude server boards like P5WDG or P5W 64 i heard those r good) i set 1.55v in bios and getting 1.536v idle and 1.524v load, but i dont think vdroop really maters that much unlesss u actually load both cores 100% for a long time, which is a problem if u actually do that cuz if ur cpu is not gettign enough vcore it just reboots, but i use my comp for gaming and when i set 1.55v i never got above 47c according to coretemp.
also for temp reporting Gigabyte = Asus reports < Coretemp = Badaxe, for some reason i get low temps on GA-965-DS3 and P5W DH according to their asusprobe and gigabyte
now back to ur question, i dont think u should go over 1.5v idle but then again no one can prove that hes cpu died b/c of actual vcore 1.6v ...