I've rode 1,000 miles several times.....on my Ultra Classics and once on the SEEG. Terrie and I have rode 800 miles days a couple of times.....me on the SEEG.....her on her Dyna once, going to Sturgis and just a month ago when we headed up to Canada, on her Street Glide.
It's not as difficult as you might think......leave at 5:00 a.m. When you stop for fuel at 150 miles, you drink a little Gatorade, maybe eat an energy bar......oatmeal for breakfast (the breakfast recommended by the Iron Butt Riders Assoc.). When you stop for gas around noon as you're filling up, she's inside getting the burger or whatever the fast food is (Wendy's, Carl Jr. etc. all have salad bars) so that the meal is ready as soon as you walk in the door. In the late afternoon you may want to have a 5 Hour Energy with your dinner meal (I used to drink the Red Bull.....till the caffene started causing problems) to help you get over the hump.
By mid day you're already in a rythum and it's "just another 150 miles......just another 150 miles, etc." and those 150 miles start seeming closer and closer together.
I'd not suggest this kind of riding your first day out......it's a lot easier after two or three days of riding. And it's certainly not sight seeing.......it's interstate freeway riding to get these kind of miles in.