I've had a RANS V-Rex for a few years, and I love it for long-distance riding. I'd say it took a season to get comfortable and in-shape. The longest tour I've done is 6 days/600 miles self-supported solo. The great thing about that tour was, at the finish I was tired but nothing hurt. With my lower back issues, that's amazing.

Like others say, ride as many different kinds of bents you can, and pick what feels best.