It's not a straight forward question to answer unfortunately, as every single 6700K and pretty much every other CPU out there have different voltage tolerances.
For instance when it comes to overclocking, one person might have success at being stable with 4.6Ghz @ 1.30V, and another person might have better success @ 1.25V but then someone else far away may need 1.38V in order to get stable at 4.6Ghz. It's all down to the silicon lottery, a lot of it is mostly down to the likes of Intel batch numbers. With regards to the lowest voltage for stock in particular, I'm sure I read somewhere that the average figure is around the 1.15V mark but again this could vary.
Liam.