I'm basing my comments on the thousands of posts I have read on this and other vaping forums as well as my own experience vaping on 15 different model PV's. Couple that with the actual physics of battery technology and I stand by my comment that a "heavy" vaper as the OP inferred, will NOT get any where close to 6-7 hours on even the larger kr808 battery. Now if the OP, or anyone for that matter, hits their kr808 a couple of times an hour, then they might get 5 or 6 hours on a charge. I believe most of us would consider that very light vaping.
After reading thousands of post where some new person states that they are tired of only getting an hour on a charge, I would rather error on the side of advising them to get a better battery model instead of inferring that a heavy vapor will get 6 - 7 hours on a kr808 battery.