Idle 1.6GHz is ~0.7-0.9V
3.4GHz is ~1.21V
4.4GHz is ~1.31V
There is no fixed upper limit on stock voltage AFAIK.
I think there was confusion about "maximum voltage" on these K chips. Intel had given a "VID range" with upper limit around 1.5V, but this was just a possible range. With the 32nm processors, the maximum SAFE voltage would need to be as low -- or lower -- than the previous generation CPU's for which they'd actually reported a "safe" range in the detailed spec-list on the INtel web-site.
What you say about voltages at 1.6, 3.4 and 4.4 seems about right to me. That is, those voltages seem to correspond to the "auto" value with the processor running at that speed and the power-saving features turned off.
but "5.0 Ghz pie-in-the-sky" and all the rave parties about it, Intel never said how much you could push these cores: We're our own guinea-pigs. I've seen people push the cores to 4.7 or 4.8, and then get into a panic about "excessive temperatures" at any speed. Even the tech-savvy reviewers were showing 1.404V @ 4.7 and as low as 1.400V at 5.0. That doesn't mean 1.4V is a safe voltage.