We have traveled as much as 8-10 hours or more in a day. But never that long two days in a row. 5-6 hours is more our normal limit. And even that gets old more than two consecutive days. But everyone is different in that respect.
On interstates and other multi lane limited access highways you will probably average around 55 miles per hour, factoring in stops for food, fuel, and rest. Secondary highway speeds will be less. Don't be mislead by travel times shown on google maps or similar. Those time are actual driving times. If you check the numbers you will find they are figuring an avg. speed in the upper 65-70 mph range, and than is not going to happen unless you never stop.
