I know from talking to a few people and from experience that once Broadwell-E hits a wall, its more like Mt Everest.
You might not be able to get more than 4.5 out of the chip full stop. That being said, 4.5 on a 6850K is around 4.8 on a 5820K, a very hard to hit number indeed, not to mention your ridiculously low voltage. You might get a few more Mhz by bumping the BLCK a notch or two, otherwise I'd call it quits.
Are you overclocking the cache at all?