For trips, figure 50mph average. Doesn't matter if it's a 200 mile trip or west coast and back, that figure has held up well for the last 20 years of my traveling. I've tried to maintain a 60mph average to make a lot of miles and find it just isn't worth the strain. Even running 70mph in my car for 220 miles from in-laws to home, we only averaged 63 mph and that was with only one quick stop for a Bo Jangles biscuit.
mleekamp has a nice two week trip planned. Good compromise seeing what they want to see in a compact time. I'm looking at 3 weeks for Yellowstone and don't think I have enough time to make it a relaxing trip.