I have rode Fort Davis area, not Big Bend. It is great for riding with very little traffic and wildlife you probably don't see often (antelope, javelina) but isolated. Make sure you have a sag or have plenty of stuff for fixing mechanicals. We ended up having an unexpected SAG for the 74 mile loop, we would have been in trouble otherwise. Have fun, remember the dry air and altitude might dehydrate you quicker but probably not since your everyday altitude is higher than mine.
I would locate the Best Road Bike Rides in Texas Book, I think your planned ride might be in there.
Amanda
2011 Specialized Epic Comp 29er | Specialized Phenom | "Marie Laveau"
2007 Cannondale Synapse Carbon Road | Selle Italia Lady Gel Flow | "Miranda"
You don't have to be great to get started, but you do have to get started to be great. -Lee J. Colan