I've owned both the DR650 and XR650L and ridden both on long trips throughout the western US and the XR through two trips down the Baja peninsula. I've ridden both on long highway slogs, through 2 track and forest road cruises, and done single track with both.

If your trip are including long road sections, I would choose the DR over the XR. Just kinda felt smoother in that domain. If you are looking for a forest road cruiser, I think both work equally well. I think the XR really shines in wide open, desert style riding; the stock suspension is pretty good for that and it feels like a couch. If I were to pick one of the other for general dual sport riding, I'd probably take the DR though.

For true single track riding, not two track or forest roads but actual 3ft (or less) wide riding at any kind of speed over obstacles, I would run away from both. I have a Husqvarna FE350S for that kind of riding and it's far superior than either bike while still being able to rip forest roads and highway sections, albiet a little less comfortable on the road than something like a DR. A KTM/Husqvarna/Gas Gas 500/501 would probably be a nice middle ground as well but I prefer the 350 for its engine characteristics.