For 2,400 miles in the summer months, good weather, lots of daylight, 2 adults, no kids...you should be able to nail that roadie in 3 days. That's not even aggressive: it assumes you take breaks, don't drive after dark, and drive roughly the posted speed limits.

Two days would qualify as aggressive but doable for 2 drivers that don't mind driving at night. I've done an 1,100 miler by myself in 16 hours. (That wasn't fun.)

All of that said, I'd start with how many days you have and work backwards from there. If your schedule allows for 6 hours of driving per day, take it and enjoy the Western USA!