One more vote for a more leisurely pace. If you can possibly extend the time, do so. If you have to shorten the trip, and you still want to see both sides of the country, consider taking a train or bus across the boring middle part. Although, to be honest, I enjoyed that, too! A bit hot and buggy, but it's the totality of the experience that matters.
Whatever you do, make the trip whatever YOU need it to be. That said, I had a friend who did a hammer-fest across the USA a few years ago, something like 42 days riding time--on a pretty long route. He said it was good, but he would limit his mileage to about 60 miles/day if he did it again. He said, and I couldn't agree more, that a cross America ride is worth doing more than once!
Have a great adventure. I consider a cross country ride one of the greatest things you can do in life!