I've been landing at 3.7x on the lowest cell. When I balance charge the 5000mAh batteries back they're taking anywhere from 2400 to 3400 mAh. That would tell me I can fly a little longer without much of an issue, based on the 80% rule (which would be 4000mAh). When I power the bird down right after flight the cells are at 3.75 or a little higher.
Here's a shot of my hexa in a test flight this evening. I just picked up a NEX-5T and got it mounted on the Arris Zhaoyun 3-axis gimbal. Some jello issues to work on, but so far so good.
For fun, I think I'm going to attach my Phantom to the bottom of this hexa and fly it around, just for perspective. That would be entertaining.