If a person were able to drive 70 MPH straight through without stopping or slowing down then you would be able to drive the 800 miles in 11 hours and 30 minutes to 12 hours at most.
However you have to factor in that you won't be constantly driving the 70 MPH all the way through as you will be stopping for gas and restroom breaks etc.
So those stops and slowing down for traffic will slow down the time it takes to drive the 800 miles.
So in ideal conditions including the stops etc it would take you around 13 to 15 hours to drive 800 miles depending on the road conditions, time at rest stops, getting gas etc.
You might also get into some road work that causes you to stop and get delayed.
So expect 13 to 15 hours to drive the 800 miles and for me I would drive 8 hours one day and then rest at a hotel or something for the night and then drive the rest of the miles the next day unless you have another drive that can continue driving while you sleep.