Not just some Andre, most of us, haha. But, rest easy, Big Bend is much easier on a big bike than Mexico, in my opinion. Most of the riding is street to dirt and return on street, and the dirt is fairly flat and easy. Except in the state park, which isn't really on the rally agenda. You'll do fine on the 1200.
Unless it rains. Then almost nothing works in Big Bend. It becomes pure slop, muck, and misery. So if it rains, you'll be on the best bike out there....easy to rack up highway miles seeing the various sites from the pavement access. All the guys like me on our little dual sports will be jealous as we pitter along and soak up the raindrops.
Historically, Big Bend (aka Terlingua) has under .5 inches of rain every January, February, and March. Only come May does it rain more than an inch a month. This year, 2015, there was 0.87 inches in 3 days...the three days of the rally, and 1.5 for the month (vs a normal 0.31)
http://www.usclimatedata.com/climate/terlingua/texas/united-states/ustx2692/2015/3 The poor desert just couldn't cope.