The DR is the equal to the Dakar on the road and better off road. However, much of this is down to rider skill. A good pilot can do just fine on the Dakar but he will work harder in technical conditions, mud, serious rocks.
Given the Dakar is roughly 65 lbs. heavier than the DR650 it may "feel" a bit more stable at speed on the highway but mostly weight is the enemy.
I just completed a 5 day ride in and around Moab, Ut. with a buddy on a very tricked out Dakar with about $3000 worth of Tourtech gack. The bike weighs in
at nearly 500 lbs. with tools, hard bags, fuel.
My DR is around 400 lbs. as you see it. (5 gallons of gas)
The Dakar gets amazing fuel economy, over 55 mpg even ridden hard. But the DR is just as fast and very stable and comfortable for hours on pavement.
The BMW is a nicer looking bike and if maintained should be OK. The DR will run forever no matter what you do or don't do. Its a tool that happens to work very well off road or on.
DR, KLR, Dakar (KTM 950 hidden behind)

The DR650 makes this easy.

Dakar headed downhill....much steeper than the pic shows
