Unless you're a "regular" used to driving long distances, 600 miles in a day is about the comfortable maximum for one driving alone. Not a regular driver and alone behind the wheel? The think of 450-500 miles as a full days drive.

In this case, 940 miles or so one way, you're talking about 4 full days on the road. I do love the Southwest, but will tell you that that sort of driving (especially as Summer takes hold) is not every driver's cup of tea.