The Sertao is a good option. I think the G650GS is a pretty good road bike. I rode mine (not a Sertao) back and forth between San Jose, CA and Spokane, WA several times, a few of those times in a straight iron butt shot. I pretty much accepted it wasn't very good in the dirt and I should have got the Sertao, but I traded for the F8 instead and I couldn't be happier.
The nice thing about medium to big bikes in the dirt is it really helps develop your skill. When I ride a small thumper or a 2 stroke now it feels like I am just floating around.
2013 BMW F800GS, Cordoba Blue, ASC, ESA, ABS
2012 BMW G650GS - 13,000 miles ***SOLD***
"If you're not mixing gas, you're not hauling ass!"
"A clean GS is a dirty shame."