Making it more enjoyable than work.
Hello and welcome to the RTA forums !
With your set up I would allow 6 days to travel and that will give you time to be able to park up for the night and get a good and proper nights sleep so that you are fit and ready to get on the road again next morning. Trying to do to much early on in your trip and plan on "pulling over for a few hours sleep" is not the way to start out, this will be a marathon and not a sprint and you won't want fatigue to set in half way through the trip. It really doesn't help having 2 drivers either, as neither will be able to get proper rest in a moving vehicle where you need to be seated and belted in, it's more tiring being the passenger sometimes and when they take over the driving who is going to keep an eye on them when the other is nodding off ? As I say, you have time for the trip, just work your stops out at around 425-450 miles per day and you can make it an enjoyable trip without exhausting yourselves. Another thing is you can't just pull up in a rest area as in many cases [most] it would be illegal. Truck stops would be OK but I think it would be nice to find at least a couple of campgrounds where you can sit down and relax at night to have a break from the road.
Interstates are built with gradual gradients and curves for the largest of rigs so you should have no problem taking the most direct route, in this case I40. If you used that extra day, or half of it perhaps you could detour to the Grand canyon for a night just to make it a little more interesting ? You don't say when this trip is starting but the further into winter you go you should allow some 'wiggle' room in case of weather disruption.