Well for my vcore running at 3.8 right now I am using 1.37v. I could get low probably I am just making sure that the cpu has enough power.
I have not tried any other Bclck aside from 175 (stable), 180 (stable), 190 (boots to windows), 200 (fails to post). The voltages were set at 1.4 vcore, 1.4 qpi/vtt, 1.64 vdimm, I have the pll set for 1.8v. LLC- ON, HT- ON, Turbo- on. I don't think it is the CPU though, I think it is the MB.