It is very possible, but it is on the faster side. Taking the straight line route will help a lot. If you are a strong rider, you should be able to complete the ride without feeling like your under the gun the entire trip. I rode the Trans Am in 65 days without ever feeling rushed or feeling that I was missing things. Expect to spend at lest one day off a week sightseeing, doing laundry and other chores, or just resting. I usually take off every 4th or 5th day.
I've ridden the first few hundred miles of the Western Express and while the route is great, don't try to ride yourself into shape over the first week. This is one where it's best to arrive at the start in good condition already. Carson Pass, less than 200 miles into the ride, can give you a very rude awakening if your not ready for it.
Enjoy your ride