From Kingman, AZ to Amarillo, TX, you would be in the Route 66 corridor. Most of the sections of Route 66 that are still in existence would be nice, easy rides with little traffic. The only big city you would go through on 66 is Albuquerque and it is pretty easy to find your way through. After you leave Route 66, you would go through Dallas and traffic there can be pretty hectic.
The worst city you will face as far as traffic is New Orleans. Traffic is heavy and it is a difficult city to find your way around because for the most part, there is no grid system - the streets kind of run every which way as is the case with many cities on the water.
I don't want to rain on your parade but five straight days of over 340 miles a day on a motorcycle is a pretty tough schedule.