The last time we had the opportunity for a longer trip out West we were driving about 500 miles per day due to limited time. We were traveling from central NC to Yellowstone in early to mid May just as Fishing Bridge campground opened. It made for some very long days where we were pretty much waking up at sun up and hitting the road only to arrive an hour or so before it started getting dark. After that we decided to keep our driving time to 300 - 350 miles per day whenever possible so we had time to rest.
We always pre plan our stops and make reservations to be sure we have a place to stop overnight. Depending upon the trip we might schedule a 2 or 3 night stop over to see an area we haven't seen but most are 1 night stays to get to our destination.