It says so in this review:
http://www.pcadvisor.co.uk/reviews/p...bridge-review/
"At the request of Intel, Ivy Bridge test results will appear on this page at 5pm, UK time."
Legit Reviews released their review early and they used 1.52V to hit 4.9GHZ,but I could not catch what stepping they used and whether other websites will get better samples.
Another thing is that E1 production samples have a larger IGP than the E0 engineering samples and have been rated at TDP of 95W instead of a TDP of 77W it seems.