Drive Time Per Day

I'm curious to hear from you more experienced TMer's on your average miles per day driving/towing on a cross country type of trip.
We've always tried to take a nice vacation every few years. For many of these years we used my car, and now use my van.
My wife and I usually try to make good time when traveling...not by going 90mph, but by trying to make few stops, eating in the car, etc. This was usually due to the fact that the ending destination was were the fun was.
In the days of the car, we have been known to do 1000 miles in a day (the car is very comfortable), and now in the van we just did 800, but it was rough, as the van is a bit more tedious to drive.

With the TM I understand that the mentality would change since the traveling becomes part of the adventure... and that towing would mean slower speeds, more stops, etc. I would also assume the "tedious" level would go way up when towing so the hours per day would need to be less than normal trip via car.

On average, when planning say a 2000 mile trip towing a TM, how many miles per day do you shoot for? Just thinking out loud, I would say that you would average 60mph for say 8hrs for about 450 miles per day. Sounds about right, or am I assuming too much?