My longest trip on the TW was from Enterprise, OR to Nampa, ID, but the back way through Hell's Canyon. It was just under 200 miles, I believe, and took about 5 hours. My best advice would be to plan a route that either has little traffic or better yet, a speed limit of 55 mph or less and no traffic. If it is going to be all pavement, consider running higher psi in your tires than you would on a dual sport ride.
Good luck and let us know how it goes.