A few issues from my standpoint.
A. Do the 800 mile day on day one. Your ability will start to drop on day 3, and that will let you arrive in better shape with a shorter day on the last day.
B. Two-lane road is a definate plus for me. Less stress from traffic, less wind buffeting, and easier more enjoyable ridfing makes for more miles covered in a day for me, and I get there in better shape.
C. If you insist on riding in the dark, do it before dawn. In my o2, it's a deadly combination with the end of a long day and reduced visibility. I typically ride from when I get up, (a little after daylight, no alarm, just leave the curtains cracked and I'm up with the sun feeling rested because I woke up gently), until I get tired or it starts to darken. Typically gives my about 750-800 miles in the late spring through early fall...
D. Very frequent, very short stops work best for me. I will actually take an off ramp, put the kickstand down at the stop sign, walk around the bike once, (acting like I'm looking it over), and ride right back on to the highway.
E. I seldom burn more than 3/4 of a tank while traveling. (see D.) It's just one more excuse to walk around the bike, only takes about 3 minutes, and I'm back on the road feeling rested and like I have done something important, so I stop for gas frequently.
F. Keep drinkin'. have it within reach while riding, or just take those short stops. dehydration makes ya sleepy too, and that's not good on a bike...
G. If it stops being a fun ride, do something different. This is NOT supposed to be a punishment. Remember that you are doing this for fun.
All the above are just my opinion, but it works well for me. The most important thing to remember is, YOU'RE SUPPOSED TO ENJOY THE RIDE. THAT'S WHY YOU HAVE THE BIKE. THE DESTINATION WILL ALWAYS BE THERE, BUT YOU NEVER GET TO DO A RIDE OVER... ENJOY THE RIDE!