I am moving from Illinois to Flagstaff, AZ, and will be driving out in a few days in my fully packed Mazda 3. I've made the drive many times before, but I'm worried this time because of the weather. I normally would take 40 all the way through to Flagstaff, but because of the heat and the full car, I wanted to get people's opinions about taking either 70 or 80 for the main part. I've driven both of the others before, but have come to prefer the southern route. I've tried a couple of different websites (TWC), but I'm not sure where I'll be stopping if I take either of those other routes, so it's a little harder to gauge what the temperature will be.
I'd love to hear people's opinions on which route they think would be the best. South, where I'm the most familiar with the roads? Middle, in the flatlands of Kansas? Or north-ish, through the mountains of Montana?