As I said, it sits around 0.875-0.925v idle (mostly with 1200MHz due to SpeedStep/EIST). On a mild load (playing a game or something) it circles around 1.2/1.3v and under full load it goes up to 1.432v and changes between 1.415-1.432v. All that measured with CPU-z.

That said, I found it quite hard to get 4.8 stable and it took me about 2 weeks fiddling wilth all the voltages and settings finding a stable setup which withstands lengthy stress testing. 4.5GHz on the other hand was quite easy though. It only needs 1.285v vCore to get stable...
I surely tried 5.0GHz, but that needs something in the range of 1.6v vCore to be stable and heats up quite rapidly. For that I simply do not have enough radiator space in my loop and so the water goes up to 42-45C in the long run, which isn't enough to cool that thing at that speed. Maybe next time with a larger case... 8)

Power draw (measured at the wall socket) is also a bit hefty on 4.8GHz: At idle it sits around ~270W for the whole system (including GPU and RAID) thanks to offset mode. At mild load (playing a game for instance) it goes up to ~420W and full CPU load with prime95 takes ~650W. Prime95 + Furmark takes up to 800W.